The value reddit users get is from viewing new and interesting content and comments.

The value a user of a dating site gets is the PROSPECT of going on a face to face meeting with another person.

If reddit engineers were good enough to make an AI to post great new great content everyday along with insightful comments and analysis, I'd still go. Hell, that might make me want to go even more often.

If I found out a dating site users were doing the same with messaging, that completely precludes me from getting the value I really want from the site, thus its useless.

There's a bit of a difference between the company owners starting conversations between themselves to create content interesting enough to attract outsiders and robots (indirectly) asking you to pay so you can reply to their messages.

The most underhand variation of all I've encountered was sms.ac (ironic acroynm) which suckered you in with Bebo-style friendspam to join their "free SMS" network, at which point your blank profile started receiving unsolicited reverse charge "flirts" from random non-humans.