There are also commercial companies spending time and money (programmers) to improve open source as it is easier than starting from ground up.
And there are (small) companies that add features to OS on request (for an hour price or fixed bill)
On the other hand there are commercial products that are just the defacto standard like WORD and Excel or AutoCAD. COmpanies use them to communicate with other companies and unless your 100% compatible you are not in business. (I recall that word on MAC and PC same version were not 100% compatible some time)
Also large corporations require that SW can be installed unattended and upgraded on thousands of PC's overnight. AFAIK the OS community don't have solutions for that (yet).
Finally there is something like trust, do you trust something that comes for free? or do you trust something you have paid for? that's psychological....