Good thing I didn't, then?
But the reality is that they have held it. So they're the ones more familiar with the territory than the Ukrainian military at this point. They've got established supply routes there. Entrenched defenses.
And if/when the rest of the invasion falters, Russian forces will pull back from their current large front towards DPR and LPR, rather than risk being largely cut off from support. Let's not pretend that retaking DPR and LPR is going to be anywhere near the same as retaking small bits of the front. Remember that most of the territory Ukraine has retaken so far has been in areas from where Russia has just withdrawn rather than continue fighting.
I mean, sure, that's going to happen when Russian forces are sustaining heavy losses; they'll withdraw. But they're going to withdraw towards DPR and LPR, ultimately.
But more importantly than any of that, I never said "surely they will hold it now". I said it wasn't unreasonable for someone to think that they could continue to hold it. Just because it's not unreasonable to think that doesn't mean they won't be proven wrong in the end.
Personally, though, I'd estimate less than a 50% chance that Ukraine will get back DPR and LPR through fighting. Maybe up to 66% that they'll get it back through diplomacy after the fighting has ended.