> that was back in the day when making an engine was much easier than today

I don't know specifically about how creating game engines was back in the day with lower level languages, but I can hardly imagine it was easier than today. I don't know of many things that are harder today than ~30 years ago when I first touched a computer, everything seemingly is getting easier and easier. Especially creating games, and for sure creating game engines. I'm not complaining, I'm loving the Cambrian explosion of games and especially indie games, but I do think we're seeing more and more games and game engines being made because it is easier today, not harder.