How do Core developers earn money from genuine improvements to bitcoin? There's no 'developers' reward' in bitcoin.
Answering 'they hold many bitcoins' only works until they sell, and it's an option open only to early adopters. Greg Maxwell lost nearly 1k BTC on Mt Gox and LukeJr most of his stash, so it's doubtful if they still hold many.
Normal people don't work for free, otherwise communism would work. Normal people work to further their self-interest. It's delusional to think otherwise. Hobby projects exist but bitcoin has grown out of that phase long ago.
Only miners continuously receive rewards, which also makes miners the only entity with a straightforward interest in improving bitcoin as it is - p2p crypto money.
The only way Core developers can monetize their control over repository is by hijacking part of miners' reward to themselves. How? By (a) preventing on-chain scaling (b) selling and promoting their own off-chain transaction systems.
Everything about the block size debacle becomes clear and obvious once you assume everyone involved wants to gain and that nobody sane works for free.
