Therefore

It has popped up organically my whole life, presumably from a lack of trust of pharmaceutical companies and government health agencies. Some risks of certain vaccines have been overvalued by the population and spread. Then there is the inorganic spread which has value on an intranational level. "If my rival is largely antivax I'm at an advantage" etc

Your only compatibility wall is the play store. If you've got the apk you're installing 9/10 times. Apk repos are great.