So just...put LPDDR on a DIMM? Or some other kind of removable slot?? I see no technical reason you couldn't.
Or, instead of soldering chips, make little LGA slots for the individual chips. I can't imagine the tiny added resistance from an extra millimeter of wire and pin surface contact would impact much of anything and even if it does, I'd rather take that than have no options when the next Windows update makes my machine a paperweight (obviously exaggerating, but it's getting there).
The reason is signal integrity. Running a high speed signal (never mind a bus of 64+ of them) through a connector is hard and takes a lot of power because the connector can seriously degrade the signals. LPDDR can be low power because it doesn't have a "memory stick" abstraction, just memory chips and controllers. It's not the resistance that kills the signal, it's the inductance and the impedance mismatching.
I think you're referring to DDR3L DIMMs, which are just a down-volted version of DDR3. LPDDR has never had DIMMs because of signal integrity issues. They take power to resolve.
Or, instead of soldering chips, make little LGA slots for the individual chips. I can't imagine the tiny added resistance from an extra millimeter of wire and pin surface contact would impact much of anything and even if it does, I'd rather take that than have no options when the next Windows update makes my machine a paperweight (obviously exaggerating, but it's getting there).