There are some good reasons for this.
The app developer gets to sell you 2 versions of the same app, one for macOS and one for iOS... which Apple will get a nice cut from.
exactly. this is all about keeping developers happy (and treating them fairly). there are lots of apps out there with different iOS & mac versions and, with the mac versions often costing 3x as much or more, being able to install the iOS version on your mac has the potential to really cut into developer revenue. take fantastical or the carrot weather app as two easy examples.
that said, not being able to run things like the nest or kasa app on an apple silicon machine is frustrating because in many cases there is NO alternative or way to run these apps on a mac. want to control your thermostat or lights from your mac? too bad. that said, the fault here is with google and tp-link for not allowing you to install those apps on a silicon mac. hopefully with a little time to polish them they will allow it.
and then there are some apps, like authy, whose iOS app runs better than the mac version on an m1 mac..