Udyr currently has a ~53% win rate at 40+ minutes in Diamond+ and this is not just due to sample size. It's true for many other previous patches too. He isn't a good teamfighter but his split-push, disruption and skirmishing make up for it. His map scaling makes up for his weak 5v5.
He's a cheesy and oppressive jungler early. Even champions with dashes struggle to get away from him and almost all junglers can't duel him early. He also tends to do objectives fast and has a massive tempo advantage over other picks.
Why would such a champion need a better late game? There are legitimately weak early game picks who aren't that good at dueling, such as Zac, Ekko, Eve, Amumu, Kayn etc. I understand why they'd have a good late game and yet some of those don't even outperform Udyr. For instance, Zac is at 48% late game in Diamond+. Amumu's late game got nerfed and he's only 1% higher than Udyr despite how pathetic his early game is. Basically, Amumu has to suffer 10-15 minutes or at the very least have great spots to use his CC to turn fights yet still doesn't win many more games late game because Udyr's split-pushing becomes hard to deal with. Ekko and Kayn are actually lower too.
Why should Udyr get nearly free late game power when his power curve shows that he's good early and mid game as is? He doesn't even have to make a sacrifice for it with greedy runes or builds. If he's going to get such significant late game buffs, he should pay for it early rather than being an unduelable raid boss that destroys pretty much any jungler he finds early levels.
Disclaimer: I don't really play Udyr and haven't tested this. This is just my very early impression and I'll admit that Udyr has not been a problem since the scuttler delayed spawn. However, I also don't feel like he's terrible and he was extremely underrated when the meta was basically all level 2 junglers.