> But why do we have such a (imho unfounded) desire to be a be able to open a file in a proprietary format from 30 years ago and expect to be able to edit it like nothing happened in the mean time?

Also largely microsoft's doing. They're big on backwards compatibility/legacy support (except sometimes for when it gets in the way of greed) and in doing so have largely trained all those people using Office Products to expect just that. It's part of their entrenchment/momentum strategy.

Doesn't help that American corporate culture in general seems to have adopted (enforced?) that expectation as well. Though that's a little bit of a chicken-and-egg situation so not sure where to score the blame there.

Like the other commenter said, lot of companies depend on loadbearing spreadsheets because it's cheaper than a salary. Not saying it's necessarily a good idea, but it happens enough that it's a known market force.