Because it is the next step on the way to exclusivity.
On the dating platform you are one of potentially hundreds (or thousands) of message chains and easily overlooked. In their phonebook you are most likely not.
If you think of apps as locations, you are switching from "meeting at the bar"(dating app) to going somewhere where you both spend more time "happily" (some other app/messaging). A lot of people used to swipe like two sessions a day, but would be texting/snapchatting all day. So you are inviting that person to be more present in your days.
It signals that you are willing to take one small step towards something vs. "just chatting on tinder"
Because you can then simply talk on the phone.
Phones are not just for texts.
Inside the dating app messenger? No idea — her right sweep will mostly result in a match so you’re competing for attention with potentially a huge number of people depending upon how much that person right sweeps. (PS. I am not kidding — this could be true even for female profiles with zero pictures, zero details :D).
So it’s a way of getting filtered up.
Okay, finally a place I can ask this. I hope you and others can explain. Why would exchanging numbers (or Snap accounts, etc.) with someone be a goal? You already have a way to communicate! I understand moving to in-person dating, but not to another way to text.
> I'd rather be quick to move to that stage, and be more selective about who I think I might want to spend a first-date hour with.
I think either you mistyped the funnel or I misread it. You make it sound like a first-date hour (or so) is given freely and first-date evenings are rarer. Which sounds reasonable, but also seems contradicted by the part I quoted.