Right, but what has become common, if successful at cornering market share, is then changing the license to something open-source-ish and charging money for what used to be free. Sometimes a lot of money.
Many swore they'd never do it. Many probably even meant it at first.
So, it's a concern for sure.
Also an option, when choosing what to use right at the startt, is being careful about using an open source solution from a for-profit startup, and evaluating all your other options, taking into account that it may not remain open source, and if it doesn't, what place it has in your business, how hard it would be to switch then, etc.