Wallets in Backpocket?

Honestly I've never understood why this is done. First of all I think it's putting you wallet at a huge risk to get taken, but as if that is not enough I think it's also very uncomfortable to sit on a FULL wallet. Chiropractors I've talked with have said this can mess up your back. But disregarding these things, people still think that this is the best way to carry a wallet..... Why??