In case of majorify of indie games you only can only get $100,000-500,000 of funding total for one game with development time of 6-18 months. And like 50%+ of this money will go into creating art assets especially if we talk of pixel art.
Go look what is the salary of senior C++ programmer with experience working with graphics, audio and little bit of everything. And one person can hardly create anything close to game engine tooling unless he work for several years.
Making own game engine is the last any game developer gonna consider.
Not everything has to be "financially viable" and return a profit. The best things in life are made by people without any profit motive at all.
It's easy to get sidetracked by "the engine" when all you wanted was to create a game... Most amateur gamedevs I know all started creating "the engine" and then the actual game never happened.
Why should "decent human people" who want to build a cool game be forced to first build an engine for it?