There are prolly more players that would buy him for 100k. So you would have competition and therefore he still costs more. If they introduce skill drop for every player release, we would get an affordable player soon, or get him to a range when he is not really desirable any more.
Why shouldn't there be a max salary?
Because it would create an unfair advantage to the top teams with good funds. How can a C with +5 in inside skills (all other skills are equal) cost the same.