I think it is because Google Play Store doesn't recognize the beta program. I certainly hope they fix it soon. I'm currently running it on my Xbox One but I'd like it on my mobile as well.
Many say it works by downloading the apk from a trusted site called apkpure . it should be in the tips section somewhere, or other sections. it's come up a lot.
there's a link in the feed that gives you a link to the 3 APKs needed and a link to the app that will combine and install them for Disney+ to work. it's working perfectly fine for me.
