I'm pretty sure I do understand the issue. Here are some facts (and an article to back it up):

1. putting memory closer to the CPU improves performance due to less latency - from 96GB/s -> 200 (M1) or 400 (M1 Max) GB/s
2. customers can't easily solder on more RAM
3. Apple's RAM upgrades are way more expensive than socketed options on the market

And here's my interpretation/guesses:

1. marketing sees 1 & 2, and sees an opportunity to do more of 3
2. marketing probably asked engineering what the bare minimum is, and they probably said 8GB (assuming web browsing and whatnot only), though 16GB is preferable (that's what I'd answer)
3. marketing sets the minimum @ 8GB, banking on most users who need more than the basics to buy more, or for users to buy another laptop sooner when they realize they ran out of RAM (getting after-sale RAM upgrades is expensive)

So:

• using soldered RAM is an engineering decision due to improved performance (double socketed RAM w/ Intel on M1, quadruple on M1 Max)
• limiting RAM to 8GB is a marketing decision
• if you don't have enough RAM, that doesn't mean the RAM isn't performing well, it means you don't have enough RAM

Using socketed RAM won't fix performance issues related to running out of RAM, that issue is the same regardless. Only adding RAM will fix those performance issues, and Apple could just as easily make "special" RAM so you can't buy socketed RAM on the regular market anyway (e.g. they'd need a different memory standard anyway due to Unified Memory).

I have hated Apple's memory pricing for decades now, it has always been way more expensive to add RAM to an Apple device at order time vs PC competitors (I still add my own RAM to laptops, but it's usually way cheaper through HP, Lenovo, etc than Apple at build-time). I'm not defending them here, I'm merely saying that the decision to use soldered RAM makes a lot of engineering sense, especially with the new Unified Memory architecture they're using in the M-series devices.