Another big factor is that devs know that startups can (and, as in this case, will) go out of business, so they’d rather go with an FOSS offering that can’t just disappear with two months to transition off of the platform.

1. You are trying to sell software to someone that often loves writing software themselves. 2. You often can't convince them that they could NOT recreate your product easily. They will pick a tiny subset of functionality and say "oh I whipped up this demo that does 90% of what we need last week". 3. They don't care about the maintenance cost of self-written. In some cases that's their job security. 4. Even if it makes them 50% more productive, their hours or pay won't change.

This is why the "best" products are often in boring areas OR have a unique platform advantage. Think of paypal/stripe.