There are probably many techniques and processes that would be tried and developed if it wasn't locked up by patents.
Without patents, there is far less incentive to seek progress. What's the point for a for-profit organization to spend resources on Research, just to see your innovation immediately copied?
And if said for-profit organization still innovate, it has a strong incentive to keep its innovation as secret as possible. Patents by contrast, incentivize sharing, on one hand it makes the innovation public knowledge, and on the other licensing agreements usually exist.
And in the end, 20 years is really short compared to human history.
Are patents an ideal solution? Hell no, this system is too easily abused (patent trolling, patent thickets, etc), and feels really wrong at times (patents on life-saving drugs for example). But so far, that's the best compromise we manage to mostly agree on in terms of worldwide IP recognition.
In tech, yes, 20 years is a lot, but that's more of an exception.
And imho, it's slowing down: A 20 years old computer, like an Athlon 64, today, could probably run most of the usual basic workloads (mail, text, word processing, browsing) with up to date software. It would be slow, but it would work. An 1983 years old computer in 2003 was just obsolete and completely unfit to run any of the usual 2003 software.