Daniel inadvertently explained why it was a bad idea. Putting money into building a structure to support dozens of distros, all the while knowing that if your program is worthwhile it will eventually be
recreated by the open-source community and distributed (and supported) for free, is not generally a part of a profit making plan.
Just because someone wrote a piece of for-profit software doesn't mean they made a profit on it. Of the tons of for-profit software you mentioned, what percentage of them would you estimate actually made a profit?
All of them--Cisco, Steam games (well over 1000 now), tons of HPC software, Oracle database, Firefox (makes of profit from advertisers, etc--not from users which are basically its product), VMware (ESX is Linux-based).
Red Hat is a billion-dollar company, profiting from Linux.
Trend Software charges a pretty penny for its anti-malware software.
BRU Backup software charges between $499 and $4,999.
Here's a list of proprietary software--all from companies making a profit.
That profit may not necessarily be a cost-to-the-user purchase price, but they are still making a profit from Linux. The business model is just a little different than you may want. A lot of the above software do charge for copies of their product. Some don't.