It's not "caving." It was never going to be a permanent hold.
But holding allowed the McConnell and Graham to show their asses about a sham, and it pressured "moderate" republicans to consider votes for witness testimony, and it allowed further things to be added (see the current Lev Parnas shit). That's about as good it was going to get, so it was a good move to hold for a bit.
Holding indefinitely would be stupid and look terrible; the public is already in majority support for impeachment, you don't want to lose that support by fucking around too much. They can see that the republicans are trying to acquit him, which is why now people like Romney are open to witnesses - they are feeling the pressure, and thus an outright immediate acquittal as was previously planned by Graham and McConnell is off the table.
Mind you, it will still be a shit show, and the republicans will do their best to paint him as innocent. But that was always going to be the case; now dems go in their with a little more power than previously thought, especially if they are able to rally witness testimony, further allowing Trump's shady/illegal behavior to hit the limelight.
Impeachment/removal support is at an all time high at the moment (
https://projects.fivethirtyeight.com/impeachment-polls/), and the dems are actually playing the political game here pretty well. But they have a tough battle ahead to control the messaging leading into the election, because that's truly the only way he can get removed.