Not much. Probably less to do with saving money and more about locking you into a specific amount of RAM. That way you spend the extra schmeckles in the first place rather than upgrading the machine yourself 2 years down the line.

It is also space. Non-upgradable ram can be put on when the circuit board is assembled, by robot. Upgradable ram has the socket installed in the same process, but then needs the ram put into the socket by low cost workers.

But as I said, space is likely the biggest reason.

In this instance, both laptops use LPDDR4x, which doesn’t exist in stick form. DDR4 SO-DIMM sockets are a challenge to fit though, so most OEMs take the easy path and go with soldered RAM there anyway.

I wonder if it's mainly an issue of finding empty space for it.