Yes, making things upgradeable generally adds weight and size to components. Sockets aren't "free", calling it planned obsolescence is absurd. They've been designed to have wired in components for a reason. You may not agree with that reason, say size constraints, but that is the constraints it was designed under. Weighting any decision is: how much will this cost our design? (note, cost here is not just money, its time, size, weight, manufacturing cost, complexity, etc...)

Upgradeability is a feature, if nobody is willing to pay for it, guess what will happen to the feature? Same thing as happened to our own species tails, they became obsolete.