What they want to do is to cash in on the popularity of Bitcoin, otherwise, I don't see any reason for a bunch of developers to try and be the next Bitcoin when if they are capable enough, they can create good cryptocurrencies and blockchains that will help people in one way or the other and they will still get their fair share of popularity within the market.
As mentioned by others, if a blockchain is fast, has lower transaction fees, lower confirmation times, and is secure, it will get a lot of users in the market because we know that people like fast and secure blockchains that they can use for their daily transactions without having to worry about rising transaction fees and congested mempools.
There really is no direct way for developers to earn from trying to improve bitcoin as there is no entity that directly owns bitcoin as a whole. However there are companies that may hire developers to try and find them ways to improve on bitcoin so they benefit from it.
I am sure many companies especially one that handles exchanges would want huge profits so if they are prioritizing that over developing bitcoin then there is nothing we can do.