Undo history getting wiped out

Okay, I asked about this back in August but never received a single reply.

I’d gone back to using 4.26 and then 4.27 and figured maybe it was just a bug that hadn’t been cleared out yet. But then I decided to come back to 5.0 and the problem is still there.

Any time I save my project, or choose build all levels, my Undo History is completely wiped out. Surely this can’t be an intentional design choice, is it? What possible reason can there be for doing this? No other software I use, or have ever used as far as I can recall, does this. Not even your main competitor, Unity.

So, can someone please, please, please, please explain to me why this happens? What other things should I avoid doing if I want to maintain my undo history for an actual useful length of time?

Thank you.