That part's the same with the skills-based immigration visa (not specific to the startup visa). The motivation is that they want people who enter the country to have enough cash on hand to be able to pay for an apartment deposit, and their initial rent, food, etc. until they get an income stream flowing. If someone enters the country with only, say, $500 cash on hand, there's a significant chance they could end up homeless and/or needing to draw on social-welfare services almost immediately if their anticipated income stream falls through or is delayed. Requiring them to have a cash cushion means the person should be able to take care of themselves even if there are some early troubles.
