There are benefits to Apple's implementation of soldered RAM. Unified memory uses less power and helps to boost battery life. A thin chassis is also one of Apple's priorities and soldered memory helps them achieve that. SODIMM slots are relatively thick. Additionally, Apple's unified memory enables bandwidths 4-8x traditional DDR4. It's a matter of tradeoffs, and there are valid points on both sides; it is not merely "defacto planned obsolescence."