We really ought to separate the fact that "open" does not always mean "free" here. Especially given that it is fairly straight-forward to change licenses on a whim.
Imagine you wake up one day and suddenly the company/OSS maintainers put out a dual-license on the project. You now have to pay $0.20 per install after your app has made $200,000 over the past year. Now you're still using open source, but still legally held to the terms of that license.
Licenses tend to be permissive enough that if such thing were to happen or other factors(discontinued development/support/etc), community forks can be created(which has its own set of problems).