This is my guess too. It's a very weird design decision, especially for a developer targeted laptop. I would probably be less unhappy with a 16 GB RAM chip soldered, but than an 8 GB one.

i get that for achieving higher memory speeds, you need to often solder instead of making it available as a slot.

but most people would like to upgrade, and if it is going to most likely work on the slower speed of the second stick, it defeats the performance point altogether.

just poor design in this case.