A browser is one of the most complex pieces of software you will find. There’s a reason why only 2.5 browsers exist (I’m counting chromium and safari as 1.5 because they are not the same but they are both WebKit). Maintaining a browser is difficult and making a new one is even more difficult.

Take Microsoft, one of/the most valuable company in the world. They had a browser (internet explorer) that has been state of the art, then they couldn’t maintain it anymore and it became a joke. They made a new one instead (old edge) with all the intention of making it a real player. Fucking Microsoft couldn’t do it and had to give up. They replaced it with a reskin of chrome (new edge).

Apple and Google manage to maintain chrome and safari both thanks to their position of monopoly, and because their position of monopoly depends on it. Firefox exist(ed) as a tax sponge for Google, but it’s definitely behind chrome in technology, but if it was a new browser, and not one order than safari, they would never be able to make it.