Soldering RAM isn't for compact size or cost or to keep you from upgrading, it's for speed. Soldered RAM can be physically closer with a faster bus than removable RAM.
Yeah, I got downvoted but the people arguing against have no idea of the speeds of the standards. LPCAMM2 offers the same exact speeds as LPDDR5x. It is dumb as a consumer to just accept soldering as an excuse from tech companies.