The count of Google Authenticator in the Play store is between 10,000,000 - 50,000,000 [1]

The MS authenticator has between 1,000,000 and 5,000,000 [2]

These stats are just for Android devices not iOS.

10's of millions of users is not insignificant. Why does the global number of internet users matter here?

[1] https://play.google.com/store/apps/details?id=com.google.and...

[2] https://play.google.com/store/apps/details?id=com.azure.auth...

It's number of downloads btw. Some might have downloaded it once and never used, some could have used for just one app, some removed and downloaded again.

Err, I thought users are deduplicated in that case (at least on android's store).

Yes you are correct they(installs) are uniques. See "install-related statistics":

https://support.google.com/googleplay/android-developer/answ...

> Count # downloads of G Authenticator on Play Store

The iOS App Store has literally dozens of TOTP apps. I imagine the Play Store is the same.