this is what happens when you dont put enough effort into your main framework
It's incredibly difficult to make everything perfectly optimized and efficient the first time around, because the second time around, you'll have significantly more experience guaranteed with whatever engine / framework you're using, in his case, Unity. When you know what you're going for, it's much easier to simply start again from scratch than to bob and weave through broken code in an attempt to fix it all.
Of course, this isn't
always the case, as it depends on how big the project is, but as long as progress is made, there's no issue in the end.