The first M1 Macs have only been available for a few months. It's quite possible 9 out 10 developers don't even own one yet and therefore can't test yet. Smart Developers don't release code to run on a platform without first verifying their code works as expected on that platform.
Furthermore, currently available M1 Macs are the MacBook Air, MacBook Pro, and Mac Mini. Not all developers are interested in these models. Some would rather have an iMac, iMac Pro, or Mac Pro which are not yet available with the M1 (or other Apple Silicon chip.) Some Developers may be waiting for an M1 MacBook Pro with a redesigned body or more ports. Some developers might be waiting for the rumored smaller sized (and maybe less expensive?) Mac Pro.
In other words, have some patience and allow time for developers to acquire the M1 Mac that best meets their needs.
Many developers are, simply put, waiting to be able to afford one.
A lot of software is made by people earning less from their dream job of coding their own software than they would any other job; and getting new hardware sometimes has a cascading effect, so suddenly you're sitting there having to bite the bullet and get that whole new professional setup that you should have had long ago.
Then it's that refactoring of the code, replacing those out of date libraries you've been using, learning a new framework, spending time researching what other people taking the same path has run into, potentially looking into making something available on the Apple Watch while you're making changes; and so on.
For a small-scale developer, especially one living a frugal life with a partner, this could be 6-12 months worth of sales going into new stuff; and 6+ months of ignoring all current work to essentially start over with a new version of their app.
And if it's a larger development bureau of some kind that we're talking about, then it could instead be that you have to redirect staff to new responsibilities; support staff having to get trained to deal with a whole new platform, support-sections of websites that needs to be updated, new screenshots, and so on.
So sometimes it really is a simple as something that can be done in under an hour, because everything just fits; and sometimes life's just structured against it. 🤷