The SIO2SD is an adapter which allows you to use SD cards in the memory card slot.
most of ordinary people are lazi, they hate to read and try things, so that bulls*** chanels just give to him most of work done already.BDM implementation is in OPL beta of next version, not in stable v1.0.0. So it is not really official yet. Like support for i.Link (FireWire/S400) and MX4SIO.
And second, there is not many programmers out there and even less peoples who cares PS2.I'm not sure if "some youtubers talk" would change that (and also don't understand why peoples seeking knowledge on youtube, discord, facebook and all this modern shit communication channels etc. in the first place ;p).
I also waiting for exFAT.