Think of it this way. Billions of people use Windows. The OS itself is not free, and despite that it is ridiculed with trackers and adware for more profits. Operating system is a multi billion dollar industry. If everyone started using a free OS tomorrow that doesn’t even have ads, the OS industry just lost everything. Sure the dev cost for linux distros would rise because of new users but that’s it. For companies like MS, dev cost would only be a fraction of what they reap yearly, so that profit will get wiped out because people don’t pay for it anymore, not even with their data.
Another example is of Uber. Uber is another multi billion dollar company. Uber takes 30-50% commission on each ride. If everyone started using a FOSS alternative that just charged say 5% commission to just cover the dev and infra cost and reap no profits beyond that, the ride hailing industry just lost billions.