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.