I am co-founder of indie game company. Like in any business there is tons of things you have to deal with: hr and managing people, making good game prototypes and pitches, finding funding or publisher, negotiating contracts, crunching for milestones and release.

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.