Great question!
As your question alludes to, there is a general pattern of eastward migration via ocean voyaging that can be observed in the Pacific. For the purposes of answering your question, I'll try couch it within the context of 'why east, not west?'
To begin, and to really do this question justice, we have to discuss the Lapita people(s). While the islands of south-east Asian and Melanesia had been occupied by humans from at least 40,000 BP (38,000 BC), population movements never made it past the Solomon Islands, with initial human arrivals in the Solomons being dated to rough 28,000 BP (26,000 BC). This raises an important point, the momentum of these Pleistocene migrations distinctively halts once the Solomon Islands have been reached. This is attributable to one major factor; the distances between islands east of the Solomons is significantly greater than those throughout modern day island south-east asia, with a lack of adequate sailing technology making further migrations past this point near impossible. This biogeographic boundary serves as the basis for the two major geographic distinctions used today in Pacific Archaeology; Near Oceania, referring to the closely located Islands of Southeast Asia and Melanesia, and Remote Oceania, those lying further east of the Solomons, encompassing Vanuatu, New Caledonia, Fiji and the Polynesian Islands.
Tens of millennia later, another significant wave of migrations was taking place throughout the Pacific. Austronesian peoples, originating from modern day South-East China and Taiwan began a rapid series of migrations ca 4000BP (2000 BC), moving southward through island South-East Asia, the speed of which was facilitated by advanced sailing technology and maritime navigation. Heavily associated with these Austronesian dispersals are red slipped ceramics, a stark addition to the previously a-ceramic archaeological records of pre-Austronesian Near Oceania. These Lapita ceramics, named after a site in New Caledonia, came to be the primary archaeological material associated with the Austronesian population that moved rapidly into Near Oceania. Lapita populations were the first to penetrate the vast ocean expanse into Remote Oceania, rapidly moving through Vanuatu, New Caledonia, Fiji, Tonga and Sāmoa. These last archipelagos were settled ca. 2800BP (800 BC). It was from the Lapita population in Tonga and Sāmoa that the Polynesian cultural complex found throughout Remote Oceania at the time of European contact had emerged (according to Roger Green and Patrick Kirch's 'Hawaiki Model'). Polynesian voyaging migrations begin around 1300 BP (700 AD) from Samoan and Tonga, eastward into the Cook Islands and from there, further eastward into the Society Islands (Tahiti, etc.) and Marquesas (among others).
So, now we get really into the question: why east, not west?
It can be assumed that the direction of Lapita migrations through island south-east Asia and Melanesia were influenced by the general eastward orientation of the region. But what about Remote Oceania and Polynesians? Without a doubt, the greatest contribution to this question comes from Geoffrey Irwin. Irwin posits that Lapita populations that moved into the Bismarck Archipelago (Near Oceania) were in the perfect position to develop their skills as voyagers by traversing the (mostly) inter-visible islands for centuries, gradually honing their seamanship to a point where they had developed adequate technologies and skills to expand into Remote Oceania. He calls this the 'voyaging nursery'.
But, particularly relevant to eastward expansion is Irwin's idea of 'survival sailing'. Prevalent trade winds blow east (or more accurately south-east) to west across the Pacific. While sailing into the wind seems like a counter-intuitive endeavor, if your goal is to ever return home, then it provides you with your best option. Essentially, if you explore in an easterly direction against the wind and find yourself at the point where you would need to return home (due to dwindling supplies, etc.) you can turn around and rely on a relatively less-arduous return leg, with the wind reliably at the rear of your vessel. Considering Polynesian voyagers understood celestial navigation through the recognition of latitude, returning to your home island isn't just sheer luck, it's tried and true strategy. Irwin's model is far more complex that what is presented here, but this gives you the jist (you can find more info in the bibliography). So essentially, the eastward expansion in the Pacific that is associated with Lapita and Polynesian peoples is likely due to the development of navigational exploration techniques.
That is not to say that voyaging was restricted to this direction. Hawai'i and Aotearoa/New Zealand are outside of the survival sailing assumptions, BUT the eastward trend in voyaging is generally explained by this strategy.
I hope this answered your question, or at the very least provided you with some avenues to explore. The question is far more complex than what can be answered in a Reddit comment, but I tried to condense my understanding into something that is easily digestible. Feel free to ask further questions
References (there will be a lot of Kirch in this):
Irwin, G. (1992). The Prehistoric Exploration and Colonisation of the Pacific. Cambridge: Cambridge University Press. doi:10.1017/CBO9780511518225
Kirch, P. V. (2010). Peopling of the pacific: A holistic anthropological perspective. Annual Review of Anthropology, 39(1), 131-148. doi:10.1146/annurev.anthro.012809.104936
Kirch, P. V. (1997). The Lapita Peoples. Cambridge, Mass : Blackwell.
Kirch, P. V., & Green, R. C. (2001). Hawaiki, Ancestral Polynesia: An Essay in Historical Anthropology. Cambridge Univ. Press. doi:10.1017/CBO9780511613678
Kirch, P. V. (2017). On the road of the winds (2nd ed., pp. 55) University of California Press. doi:10.1525/j.ctv1xxsng.11
Sheppard, P. J. (2011). Lapita colonization across the near/remote Oceania boundary. Current Anthropology, 52(6), 799-840.