No, everyone is free to start a bandcamp alternative that does not sell out. But the probability of people wanting to "cash out" or trade equity for other things they want is pretty high. And so that is the world that we see, because it is a reflection of what people want.
I don’t know how to combat the shift to a single monopoly/duopoly in every market though, but it’s definitely going to make our lives worse. Especially with the erosion of private ownership for us plebeians.
Bandcamp is absolutely a company I would've considered working for. I'm long past the point in my career where I care about a lottery ticket. They were profitable, big enough to be sustainable, but small enough to be nimble. The management seemed to make all the right noises regarding their values and motivations.
I'll take that over a massive tech company or a tiny startup any day of the week.