There's a bit of a misconception in your question, since Europeans were not ignoring Africa. Portuguese and Spanish salve raids on the Canary Islands started as far back as the 1340s and by the early 1400s the Spanish had establish a permanent presence on those islands. By the mid-1400s, Portugal was trading and slave raiding along the Senegalese coast, and by the late 1400s they were doing the same off the Ghanian and Benin coasts. Bartolomeu Dias would reach the as far as the Cape of Good Hope in 1488, which Vasco de Gama would sail past to India a decade later. Other Europeans would follow.

Hostile raiding by Europeans, however, soon found itself limited. Thornton's Africa and Africans in the Making of the Atlantic World notes that

it was not long before African naval forces were alerted to the new dangers, and the Portuguese ships began to meet strong and effective resistance. For example, in 1446 a ship under Nuno Tristão attempting to land an armed force in the Senegambian region was attacked by African vessels, and the Africans succeeded in killing nearly all the raiders. Likewise, in 1447 Valarte, a Danish sailor in Portuguese service, was killed along with more of his crew when local craft attacked him near the island of Goreé.

While the European ships, designed for the high seas, both stymied boarding parties and allowed their crews to effectively flee (aided by cannons), the resistance of Africans along the coast effectively halted free movement by Europeans. What instead developed were trading contacts with local rulers and officials acting as middlemen. The Europeans would establish trading forts up and down the coast, paying fees to access already established trading networks. This sort of system would remain largely stable until the 19th century when greater European aggression would be coupled with improved firearms, better artillery, gunships, professional armies, and a much better understanding of the political world of Africa.

Europeans also encountered fierce resistance in the Americas, but entered into that world with an advantage in military technology as well as introducing cavalry. There was, of course, also the advantage of introduced disease, but I would point you towards Beyond Germs: Native Depopulation in North America for an understanding of how these were an important factor, but not a monocausal explanation for European conquest in the Americas. This contrasts with the situation in Africa where the disease situation was one which was inimical to Europeans, which meant they often had to operate by proxy, using allied local peoples for trade and warfare, until advancements in medicine in the 19th/20th century allowed for better survivability of infections like malaria or yellow fever. The Americas also had regions where Europeans crops could easily be transferred and prosper, unlike the tropical soils of West and Central Africa where Europeans would be dependent on local agricultural knowledge (as an aside, Carney's Black Rice: The African Origins of Rice Cultivation in the Americas is an excellent book about how important African skills were in the Americas).

So no, the Europeans were not ignoring Africa; there was a long history of interaction. African resistance, however, was more effective than that of the Americas. To quote Thornton again, this time from A Cultural History of the Atlantic World,

The Spanish were able to conquer, within a century of their arrival in the Caribbean, virtually every major state structure in the Americas... But in Africa it was quite the opposite. Europeans did not have sufficient military advantages to make conquests, and indeed, could not easily even land on the coast. In striking contrast to the Americas, Europeans did not succeed in conquering even on e major African polity; the closest they came to this was taking about one-half of the territory of the Kingdom of Ndongo from which they built their colony of Angola. Even there the old rulers of Ndongo managed to hold considerable territory and wer enot brought into either meaningful vassalage or replaced until the mid-nineteenth or even twentieth centuries.

The irony, however, is that European colonial successes in the Americas drove further European investment in Africa, particularly in the slave trade. So it's not really correct to think of Africa, Europe, and the Americas as independent objects, but instead as part of interdependent system of human interaction.