Most companies do not want to deal with the hassle of finding someone to perform support/bug fix work on their software. They want to be able to call up a vendor and get an answer today about a bug fix or support. Most open source projects do not have this level of support.
That's also a selling point, though, especially if you're a small company. Knowing that they weren't locked in to us, and therefore helpless if we closed or pivoted, helped sell our services many times.