The Mac etc is what Jobs wanted. A sealed beige box that only did what Jobs envisioned it to do (produce a GUI and look good).
And yet variants of the Apple II kept outselling the Mac all the way until the II was unceremoniously dropped.
He was also responsible for NeXT. That company was about trying to make the power of Unix more mainstream.
Modern Macs are far more decended for NeXT computers than they are from the original baige box >= system 9 Macs.
This in much the same way as Linux use used just about everywhere these days, hiding behind a myriad of custom UIs.
When Jobs founded NeXT in 1985 there was no standard GUI layer for Unix. What you’re referring to as the “base layer” was all of Unix.
X was only started in 1984 I believe and Sun also has a competing incompatible alternative at the time too.
It wasn’t at all clear that the X Windowing System would win out as the dominant implementation.
Although that was mostly due to price, not expandability (the Mac II with all its slots and RAM expandability was introduced 6 years before the Apple IIe was discontinued)
That was mostly school purchases.
If you want upgradeable hardware then buy the Mac Pro since it was the model designed for that purpose. Otherwise you need to understand that upgradeability comes at the expense of thickness and weight since those clips/sockets take up valuable space. And people that want upgradeability simply aren't Apple's market. Go buy something else instead.
You might be able to purchase a replacement SSD for someone like OWC or upgrade to the higher spec Apple sourced GPU if you bought a low end model but Apple is not expecting you to do this.
You can update the RAM or use external thunderbolt peripherals but that’s a long way from the older “cheese grater” Mac Pro.
If I was to guess I would say that this deliberate removal of upgrade path is actually about design for reliability.
If you remove the upgrades you remove the chance of static damage or use of faulty parts. Also the case is easier to manufacture and more robust because it’s less complex.
I think that’s the real reason the SSD is now soldered in the current MacBook Pro but it’s just a guess.
Granted, computers have changed a lot in the intervening years, but it still makes me sad to compare what Apple was to what Apple became.