> Why would they join a small company?

Once the basic needs are met, many smart and talented people look for internal motivation. It doesn't matter if it is a small or a large company, as long as they are happy and satisfied. According to Daniel Pink's theory of motivation [0], there are 3 aspects of intrinsic motivation: 1. Autonomy - trust them, don't micromanage, let them take decisions 2. Mastery - allow them to get better and acquire skills 3. Purpose - give them a meaningful purpose and sell them your vision

Internal motivation may mean differently for different individuals, but I believe the above three aspects cover the most of it.

[0] https://en.wikipedia.org/wiki/Drive:_The_Surprising_Truth_Ab...

There are lots of reasons for choosing a small company over large ones: interest in the field, involvement in decision making, maybe more technical freedom, less bureaucracy ... I would say it depends more on the company itself than its size