Its really worth thinking about the fact that more or less a single person has developed a software that has all the core functionality of Twitter... a company that has been bought for 40bn $ and used to have nearly 10k employees.
So what are these other developers doing exactly? Sure, some need to run the service itself and Twitter is probably more optimized than Mastodon, but by far the most of these people work on the advertisement part of Twitter.
Imagine a TV station having 99% of their workforce doing advertisement only...