Ehhhh, it looks like you're talking about MCU Hulk, and in the MCU, he isn't shown to have that kind of near infinite scaling.

To the contrary, he's shown as having limits multiple times, though they are absurdly high.

Besides, Thanos in the MCU is shown to have the kind of near limitless power needed to match the Hulk, it just isn't in raw strength of muscles. His power is kinda nebulous, but he kills literal gods, including Loki. And, if you'll recall, Hulk bashed Loki around against hard objects without managing to kill Loki in the first avengers movie. Thanos killed Asgardians like they were flies, with no detectable injury.

Now, you could argue that Hulk was holding back so he didn't kill Loki. And that's a possibility, but it isn't canon because it wasn't explicitly said during the movie (and, afaik, by any of the cast & crew afterwards). Since Hulk (and the rest of the avengers as well) was perfectly willing to kill the chitauri during the same movie, it doesn't make sense he would hold back against the entity in charge of them.

So, you have an in-universe example of Hulk not being as powerful as Thanos, even if that limitation is only the willingness to kill.