There is not a great deal between the averages, the difference is, at this stage Handscomb average is heading in the right direction whilst Carey's isn't.Have you seen him 'keep'? It would cost us a heap of runs in dropped catches, missed stumpings and extras for potentially a few extra runs with the bat. Heck it might even put some pressure on Pete's batting that whilst impressive for a couple of games recently arguably isn't even 100% proven at ODI level.
One of the most ridiculous suggestions I've seen on here recently. Might be able to get away with it in a T20 but 50 overs? No, just no. Want Carey out replace him with another proper wicketkeeper.
edit - Carey averages 3 less runs than Handscomb from one less game.
Handscomb averages over 50 for the Indian series at a SR of over 100.