Shadowrun is, in fact, a post-apocalyptic setting. The Great Ghost Dance, VITAS (one AND two), UEG, the Crash of '29... all of them reduce the population by huge amounts. The Crash goes another step, destroying a ton of data, and what data it didn't wipe out, it almost certainly turned into a Black IC minefield. So there is a degree of Lost Tech, though it is not as widespread as other settings.
Unrelated tangent - I find it hilarious because when I first read the Shadowrun stuff in 2000-ish, I thought 'That's stupid, because they'll have books and hardcopies of data and shit, society will bounce back', and now, I'm all like 'give me digital everything, books are heavy and kill trees'.
One of the earlier Shadowrun novels (Shadow Play, by Nigel Finley) actually goes into what happens when some of this lost tech gets discovered - war in the streets as the Megacorps start breaking corporate law, because whoever gets their hands on the tech will be so powerful/make enough profit that the legal fees don't matter. Or maybe they'll just have the tech to nuke the court in orbit and every other mega's headquarters, and not have to deal with any of it.
It's not so much that it was written in the late 80's being the problem (because, again, this is a book that the core has details for wrist-worn, or pocket-sized computers, and a smartphone type pocket secretary that has matrix capability, even... so tech miniaturization is clearly there, and Matrix 3 gives you even more ways to tap that tech into the Matrix wirelessly). The problem is that SR 1-3 all recognized the thematic reason that the matrix was setup the way that it was - to stop another Crash of '29/Super Virus from happening. A virus that just cuts through our current, and eventual future protocols. So it makes sense that it doesn't follow our current computer logic.
Now that theme is out of the way, the rules for it all? Are a fucking nightmare. So I get why the RULES needed an update. The first three editions had things that were broken, and instead of fixing them, they decided to just add on new rules to patch a thing, but didn't actually fix anything, aside from just add more broken stuff. So I can appreciate 4 and 5 changing that way. Unfortunately, I have to actually sit and play a game before I can talk full on balance, and the only MU out there is SR3.