I think, because Corp. In Corp, they want someone to be in charge, and take reponsible when something mess up. It is easy for IT to proposed to buy a solution, because the vendor take responsible for mess up, rather than use open-source and have to fix bug themselves.

There are also case where developer push malware into open-source.

Who really pay for Adobe pdf suite ?

Really I can find many open source solution that can edit PDF, even OCR the PDF for free (you might need to run OCR engine with your CPU, or pay for OCR service)