Answer:
There are many reasons some are==
1. The larger kingdom who set sail wanted to take over smaller kingdoms so that they could annex their kingdom/empire.
2.They wanted to gain better understandment of the world;in aspect of knowing earth is flat;;
3.Wanted to gain better tools and wanted to discover something new.
4.(from my aspect) They might've been exploring to increase their population since most of them generally ended in native places;.
