Because #1, there's no big payday for them if they did it, and #2 they'd instantly get exposed for the frauds they are, and #3 the suckers come to them and not the other way around. In that way, these charlatans have willing victims to fleece begging to give them money in exchange for a supposed ticket to heaven.
Cashing in by exploiting God's name in vain is worse than those check cashing scammers picking on folks who would be hit the hardest from the accrual of debt these crooks would put them in, much like those loan sharks who prey on the downtrodden, desperate and gullible.