Dating sites did not multiply them. These scammers, liars, and cheaters simply use technology just like everyone else.
One might ask:
Why are there so many "gullible people" on dating sites?
Scammers and con artists go wherever it's easy to find a mark!
Each of us (chooses) our own friends, lovers, and spouse.
Each of us has our own "must haves list"
Each of us is responsible for having our own mate selection/screening process.
(Nothing happens until YOU say: "Yes!" to someone)
Anyone who is having one bad dating experience after another probably needs to reexamine their mate selection criteria.
Whether one meets a stranger online or offline they should use good commonsense! Trust like respect is (earned) over time.