It's not the money - it's the ability to spend the money on the roster. I will grant you that the $1 million limit, which is a few years old at least, is probably too low. But, it's not a small benefit - especially if you are looking at losing the player anyway once his contract is up.
There have only been a couple of big transfers in the last couple of years: Miazga (E4.6 million) and Gonzalez (E3.8 million). The rest have been less than E3.0 million.
I understand. But let's say we receive $667,000. That doesn't allow us to replace a player of his caliber. Look at Seattle, LA and RBNY right now. They all sold on the player. Their replacements (Van Damme, Collin specifically) are markedly worse than who they replaced. If you sell this kid from $5 Million and MLS keeps $2.5 Million. We get $667,000. Maybe that allows us to buy down a guy of Diskerud's quality. But you're not replacing a $5 Million rated player with $667,000 of allocation money. Just not happening.