They are tradeable and resellable which is a very important property for poorer gamers instead of rich collectors like us.

Edit: Switch 2 is also biggest proponent of SD Express. Any supporter of SD cards coming back to phones and other devices should appreciate the stance taken here. Nintendo could've gone the Google/Apple route and just sold 512GB and 1TB models. Instead this effort, like Sony's Xperia phones, are completely unrecognized.

I wonder if the SD Express will be taken advantage of in the switch 2 homebrew scene which seems inevitable now.

SD Express is PCIe express after all (also a possible attack vector in itself, see DaMAgeCard). With nvidia drivers for Ampere already on board maybe someone will get an RTX 3090 running on a switch 2.