But I don't think you quite understand what a conversion is.
It is not merely intellectual consent but encounter with Christ and response .
So how come the only people 'converted' - using your definition are those brought up to believe the in the faith claims of christianity. Surely if 'conversion' is as you say then everyone, regardless of their upbringing, would be equally ripe to this encounter. That they aren't suggests one of the following:
1. Jesus ignores people who aren't cradle christians
2. The faith claims of christianity are only believable to those told to believe those stories from childhood
3. An 'encounter' with Jesus is only possible to those who have had that 'suggestion' inculcated from the earliest of ages - in other words not a real, external encounter, but all in the mind of a pre-existing believer.
The first (which is the only one consistent with an actual encounter with Jesus doesn't seem plausible. Firstly as there are occasional, but rare examples, of people not brought up christian converting - did Jesus misunderstand that these people weren't cradle christians, and if not why them and not others. And secondly - surely if Jesus wanted impact he'd largely ignore those brought up in the faith but focus on those who aren't already part way there.
But in the most extreme case this simply never, ever happens - there is no example of a non-contacted community (i.e. a community who will never have encountered people who believe in christian claims) who independently come to that belief. Christianity is always transmitted by people, never directly by god/Jesus. We never see a tribe that has never encountered a christian before discovered to be worshipping Jesus. Why not? If Jesus can communicate directly, why not directly with a non-contacted community in the Amazon - yet never happens.