Building a free (as in beer) engine for others to build great browsers on, is a pretty thankless task. Individuals may take pride in such a task, but for a company that needs to pay their staff, it’s a fruitless endeavor. I assume it’s much harder to earn money, if people are not using your software itself, but the forks that add all the cool stuff.
Okay, but khtml was part of KDE, so I guess it wasn’t developed by a company that needed to make money from it, was it?
And neither is chrome. Google doesn’t need it to create revenue. They need it to control the channel with which people access their main product - advertising on the web. And for that goal it is beneficial to have it as widespread as possible, even in the form of derivatives.