You aren't wrong, Apple is able to do this because implementing LPDDR is much more efficient from both a transistor and power consumption point of view, and is actually faster too. The tradeoff is you can't put 8 or 16 dram packages on the same channel like you can with regular DDR, which means that the M1 Max genuinely has a 64 GB limit, while a DDR system with the same bandwidth would be 1 TB. Fortunately for Apple there isn't really a market for a laptop with a TB of RAM.