SD and microSD nominally inhabit the same space, but microSD is effectively limited to storage whereas SD can be used for other things; it's just more flexible to provide an SD slot, if you can spare the lateral space. Among other things, microSDs are so tiny that it is often more practical to put them in an SD adapter whenever you need to handle them. That's why SD adapters are so widespread, and you'll likely find one in the package whenever you buy a consumer microSD.

Yeah, that's a bit weird actually. I looked at my country's most popular comparison site, and listed the top-10 best viewed memory cards. Of those 10: 9 microSD, 1 standard SD.

https://tweakers.net/geheugenkaarten/vergelijken/#filter:q1Y...

You can get an SD case for a micro SD card for less than 5 bucks. Can't adapt the other way inside a slot.

It's actually coming free with most off-the-shelf microSDs. And exactly that - SD as a physical format is more flexible, nowadays it can be used even for non-storage cards.