That dateline would be for the exact purpose of covering Kiribati, one of very few nations which uses the time zone of UTC+14, and I think the only nation which uses that timezone all year round. This is why the dateline is a weird shape there, it is extending to cover each of the individual islands within that nation. They get to celebrate New Year before anyone else because of this.

This was a decision made in 1994, to unify the timezone across the islands, which previously straddled multiple different time zones and created confusion and difficulty due to the country being in two different days at the same time prior to this change, depending on which island you were on at the time.

Basically, the International Dateline takes a weird shape for administrative reasons. Not all nations strictly follow the region they technically fall within on the dateline for the same reason, particularly for large nations or nations comprised of multiple islands which fall under different zones. It can become difficult for administrative purposes, and economic organisation purposes, to be attempting to keep track of all the times in all the zones you are in. Essentially, it becomes easier to manage if you just use fewer regions which are close enough than if you strive for exact accuracy. For example, China spans five different time zones, but for administrative purposes the country just uses one time zone, Beijing Time (UTC+08:00).