That should be a decision made by Telegram not Apple.
It may seem unfair and counterintuitive, but I suspect that there is non-zero portion of Apple users that happily subscribe to this model.
What we're discussing here has strong political flavor, but this isn't the only case of Apple censoring Telegram's content. For example, all even remotely pornographic channels have been banned in native Telegram apps on iOS for years. Somehow Durov is silent about this (probably because you can't score some cheap publicity over defense of pornography).
His double standards aside: parent buying his child an iPhone is probably much happier due to this policy than not.
But I don't use Apple iOS precisely because of their ridiculous grip on the ecosystem - even though from a technical perspective Android is pure garbage.
Telegram doesn’t have to follow the laws of Belarus, whereas Apple who has a presence there, does.
In this situation, Mr Cook, a man running world's most valuable company, decided to part with virtue, and become a man without honour.