I think you're referring to these guidelines: https://support.google.com/googleplay/android-developer/answ...
We did go through the guidelines to make sure our app would be eligible for auto install. For example our download size is sub 100mb. I can see in Google Play Console that all our installs are Android M+.
There are some factors I can't verify. For example, where can I check what Google Play Store version users are on?
If certain factors make a device ineligible for auto install, then maybe these devices should be excluded from the ad campaign to help ensure developers are getting good value for their ad dollars?
It created such a negative first experience for us on the Google Play store, which is a shame as we'd of been happy to invest in install ads and Google would of made a larger return from us over time. The low quality of support gave us no path to at least share our concerns with Google.
In the docs it makes it clear that there are a bunch of caveats to the auto installation. Reading through these caveats, they are all there for good UX reasons, essentially to ensure that what gets advertised is what gets installed (no bait-and-switch), and that users are going to be ok with the auto-installation (doesn't eat all their data or battery life). There is advice on how to improve eligibility, it's not clear if the author followed this or not.
The eligibility factors will vary from user to user, and may between user bases as well. For example if you have an app that is popular with users on devices with less storage space, there are likely to be more who can't install it because they don't have enough space.
One or more of these factors may not have been met for the author/publisher of this app, and it's also possible that their target market also doesn't meet the conditions for auto-install as much.