I did a rough estimate of all the people I know and the number of those people who would want to root their phone. It’s not a big number but it’s way bigger than “a fraction of 1%”.

And it’s a completely different demographic than those would would fall for the phone call scam, but it’s incredibly disingenuous of you to suggest that the only malware distribution vector is being tricked into installing an APK.

I know people who are interested in modding games, pirating software, and installing “cool” apps just for the novelty. I would argue the most likely reason those people installed malware is voluntarily, because they searched out a hacked version of Bloons Tower Defence. Not because they “needed to pay an outstanding Windows service bill”.