That is not true. There are parts of the world where Iphone use is quite low. For instance in India which is expected to have more than 820 million smart phone users by 2022, the percentage of IOS users is around 3%.
Sharechat app which is very popular in India (160+ million active monthly users) was first launched only on Android in 2015 and the IOS app was launched as late as May 2019. So yes, there was a period of around 3+ years where a major messaging app didn't have an IOS app. Their IOS app would not have added more than a couple of percentage points in terms of additional users.
Sharechat app which is quite popular in India (160+ million active monthly users) launched their Android app in Oct 2015 and I believe their IOS app was only launched in May 2019.
https://www.statista.com/statistics/262157/market-share-held...
In China with over 850+ million smart phone users, IPhone users are about 13%. https://www.counterpointresearch.com/china-smartphone-share/