Did Redis, Elastic, Mongo et al pay for Linux development, or glibc, or their text editors, or compilers, or ...? Why should they get the financial benefit from building on top of others' donated work - and claim to be an equal participant in the FOSS ecosystem - and then be peeved with others expect the same in return?
If Mongo were a closed, proprietary product who wanted to be paid, sure. I happily pay for Apple stuff, for instance. But saying "hey, come use our FOSS project!" and then pivoting to "...as long as you pay up!" is extremely disingenuous.