There are always tradeoffs for using sockets - on one hand, they take more physical space and the metal-to-metal connection required can degrade over time compared to soldered parts (the "press-fit" connection can become less than 100% reliable whether from oxidation/etc or components getting jostled slightly out of alignment from numerous bumps over time), on the other hand, they allow upgrading whether it's because you now need more space than when you bought the machine (or prices have dropped enough to make additional space a sort of "why not" situation), or because the parts fail (SSDs will wear out over time, even if that's a very long time).They do for the Mac Studio and Intel Mac Pro (in which the SSD controller is on the T2 chip so it uses raw flash like the M1). Unlike the LPDDR RAM, I don't think there's any technical advantage to soldering in flash - I guess there's just a critical number of the highest-spec SSD options you have to sell above which soldering them in becomes cheaper than using modules.
I can totally understand soldering in the flash on phones and iPads, because you're dealing with a very sealed box that's roughly a quarter inch thick (with the screen taking a portion of that) - extremely space constrained - but I still wish they'd put the flash (even if it's proprietary raw flash modules) in sockets in the laptops, so that it would be possible to replace them in the future without replacing the entire machine.