Slots arw for upgrades, repair and salvage. Almost no nowadays notebooks with soldered RAM have additional slot. What of RAM takes 2 secocds with slot. Soldering lots of pins or reballing requires specialized equipment and skilled (and expensive) person.

I'm going to scrap 120 almost mint condition 8th gen i5 Thinkpads thanx to 8GB soldered RAM, which is no longer enough for efficient office work on W11 + basic corporate background apps.

With 1 fookin RAM slot, these notebooks would be perfectly fine for another 5-10 years.