It's not just Adobe & Microsoft either. Lots of large companies with "product lines" do the same thing. e.g., an office equipment manufacturer might prefer that

It's not just Adobe & Microsoft either. Lots of large companies with "product lines" do the same thing. e.g., an office equipment manufacturer might prefer that your entire office runs on their machines, even if it means that some of their machines have to sell at cost, or as a loss leader. If everything from paper printers, to bulk scanners to ID card printers are all sold by Acme into the same corporation's offices, it makes it much harder for AcmeCompetitor to get a foothold. I used to work for a company that had a couple of "me too" products that they barely made any money on, but it was worth it to them to block a sale to the competition.