there are two reasons obviously:
1. stable engine with fixes is most important part of server. more stable and more features: you are getting unique among other servers. Profit++
2. reporting issues is not easy right now: you have to spend around 15-30min to correctly describe and show problem to others. Some problems are also very hard to reproduce and you just don’t know the real reason why something is not working/crashes. and it’s rather rare your problem is fixed within 6 months if problem is more complicated=you feel it was a waste of time
And again, if you manage to fix it by yourself - you get advantage and probably more money because of that. There is completely no profit in working on open-source tfs: at least not for bug reporters/but fixers. Maybe you, people with permissions, got some % from donations
I would love to share my thoughts about tfs but I am not really into describing in details every problem I have spotted, because I don’t have time for it: I have family, busy work, own projects. But I would like to help somehow anyway, due to 15y sentiment to ots. This is why I have learned programming