It might not be the engine. Some companies just don’t care much about optimization when they can just tell their players to buy better hardware.

Take GTA5 for example. It had a notoriously long load screen when starting up. Ranging from 2 minutes to 10 minutes depending on the read speeds of your storage drive. A modder ended up finding the problem. The code to load up the items in the game opened and read a file, but there was a bug that caused it to read through the entire file for each item loaded. The file was being read thousand of times. The modder changed one line of code and the loading time was reduced significantly. This was a bug that plagued GTA5 for years, caused by a single line of code, that the company didn’t fix because their fix was to buy better hardware.