I wonder how hard (easy) it would be to swap the parts between them, given that these are (mostly) still PCs, and determined people have done some pretty amazing things to other pieces of Apple hardware:
https://www.ifixit.com/Teardown/MacBook+Pro+13-Inch+Retina+D...
https://www.ifixit.com/Teardown/MacBook+Pro+13-Inch+Touch+Ba...
Not a lot has changed in the past few years. Macbook Pros are NOT easy to mod/change or swap parts. This is very clearly the intention of Apple.
Of course, but that hasn't completely stopped determined people from trying (and succeeding) --- look at the link I posted to where someone added a headphone jack back to an iPhone.
As long as the dimensions are vaguely compatible, the guts of the touchbar model might fit into the non-touchbar case. Some machining and creativity required.
The only downside is the cost (unless you somehow find salvage parts), but someone who really wanted to could do it.
And high stress tolerance. I mean, if - per recent HN thread - people obsess over putting a CPU into their PC because it feels like breaking a piece of expensive electronics, I can only imagine what a Macbook owner feels when applying a lathe to their prized possession...
I don't think they've done it on purpose, this is just how it has ended up because of other priorities. I think their priority is tight packaging - across every hardware line they have, doing that well has allowed them to ship more hardware features (and/or more battery life) in a smaller package that anyone else. Designing in user servicability would get in the way of this.
They may be happy that not being able to swap parts is a side effect of this, but it'snot the priority.
But: 15W TDP CPU; RAM&SSD not soldered; USBA, USBC, HDMI, SD, SmartCard and even Ethernet(!).
Or the HP Elite X2 1012. Surface-class tablet/convertible with similar specs, but...well, 10/10 on iFixit.
Sure, those devices may have other issues (that trackpad on the Lifebook...), but tight packaging is not an excuse for unmoddability.
Just you wait for the class-action lawsuit when people's logic boards start failing and there is zero hope of pulling any data off the dead drive.