Some scholars believer that people from asia arrived in the americas about 15,000 years ago. according to this theory, what was the reason these people come?

The reason for why they wanted to come is:
-they were looking for new land, new resources that they wouldn't have to compere for with other humans and which would be potentially better

The reason why they could cross the sea from Asia to America is that the sea was either frozen over or more shallow (because it was frozen in other places) - which made the crossing easier.