Making a browser isn't terribly hard, and there's dozens of 'browsers' (see nyxt, qutebrowser, vimb, brave, vivaldi, etc). Making a browser engine is hard, and expensive, which is why all of the alternatives i've used are either chromium or webkit based. The webkit ones seem to crash on anything with complex javascript. The chromium engine ones work great, however that doesn't stop Google from making changes to the engine which people are up in arms about.

Browser engines are very, very, very, very very hard to make and maintain.

See: Opera and Microsoft Edge, which formerly ran on bespoke engines until they converted to Chromium because no one would support their browser.