The truth is, unlike with RAM, it's still cheaper for the other laptop manufacturers to have a single motherboard SKU which they can later plug whatever cheap COTS SSDs they can get from various sources rather than waste effort tayloring a motherboard for a specific SSD controller, specific DRAM cache chips and specific Flash chips, as that gives them way less flexibility in component sourcing during production lifecycle and more expense in board design resulting in more expensive products with no extra margins for them.

Apple can do this economically as they have a very tightly controlled supply chain with high volumes and due to the little variation in SKUs so they can just use the same SSD controller on all their products and just change the amount of Flash chips soldered on the board and call it a day.