Yeah, the problem is most consumer motherboards don't come with that many PCIe lanes. Building storage servers for home use with M.2 SSDs is just not feasible.
PCIe is a switched protocol. We ought to have had better options to make better use of the limited lanes by now. There are a few cards with switches that can give you multiple M.2 slots on x4, but that's only with gen3, which the latest GPUs won't init on, and trying to cable that is hell. Better PCIe switch options for external enclosures exist, but aren't available to mortals that I've seen.