Interesting question! Yeah, nostalgia or... inertia maybe? I think the original synthetics were developed as “legal highs” and thus filled a particular demand for “smokable leaves that get you high” as a substitute product for weed.

And when you think about it there are practical advantages.

The form factor is not bad, compatible with your existing lighters, papers, pipes and so on and takes up “the right amount” of space (harder to lose but still concealable). Lungs are an excellent drug delivery system. You can also use it out in the open since there are existing (legal) things it could be.

You could distribute it “pure”, but it would be a lot more fiddly (tiny bags) and require a fragile (and suspicious) glass pipe, lightbulb, alufoil or what-have-you. Harder to maintain for your “addict on the go”. From a marketing perspective, much more threatening (crack/meth associations).

“Injectibles” have similar (but worse) downsides.

A pill, or snortable powder could work? Probably these do exist already - lots of dodgy pills around, some of them are bound to have these actives. Generally slower onset though and less of a high than smoking the same thing. Also somewhat different market.

Have not seen synthetic edibles or oils but no reason it couldn’t be done.

If you were going to “startup the heck out of it” you would probably go for some kind of juul-like vape. Subscription, of course....

To enable them to be smoked cheap and easily - which in return means the user feels the effects almost immediately. Same reason why majority of users smoke rather than eat cannabis.