Microsoft have literally abandoned maintaining their own browser engine. If staying independent of Google isn't affordable and worthwhile for them, who could it be affordable and worthwhile for?
Microsoft abandoned their own browser engine for business reasons. I feel like it should be obvious that what's "worthwhile" for a for-profit organization is very, very different than what's "worthwhile" for a non-profit, individual, or group of open-source developers; "affordable" isn't even in the picture.
KDE have also abandoned writing their own browser engine. Mozilla continues to produce one but they continue to attract very few outside contributors and rely largely on Google for funding. If no-one's actually doing something we should be wary of blithely assuming that it would be esay or even possible.
The fact that operating systems maintained by small organisations are more viable than web browsers maintained by small organisations should tell you something about the complexity of the web stack.
This line of reasoning is entirely invalid.