That's the thing, because it is open source it's much easier to offer money to get a fix because you have options. Hell, you can fix it yourself!
If the software is proprietary, good luck with that. The proprietary originator might have even went bankrupt and the source code lost in the chaos. Hell, the whole idea that you'd trust parts of your critical business systems to a random external vendor with different business interests is crazy.
Actually, this exact reason is why many of the larger organizations use FOSS over proprietary software these days. FOSS gives a piece of mind that is impossible with proprietary software.
normal "users" do not write software and would not have a clue how to even start to "fix" a program.
and who do you pay ? if the project has say 12 folks who work on it who do you pay them ? and who do you talk to ? really ...
sure things like a business going under happen... but i can't even count how many times i used to deal with folks in the open source world who were no help at all / had attitudes that stunk etc...
there are for sure a lot of good folks out there who are helpfull but it's a mixed bag.