The opposite is true for the tiny arms. The arms are not tiny because it’s beneficial for them to be that small. They’re tiny because there’s no reason for them to be big.
It is theorised that it might actually have been an advantage to have smaller arms, so there may have been some selective pressure:
“What if several adult tyrannosaurs converged on a carcass? You have a bunch of massive skulls, with incredibly powerful jaws and teeth, ripping and chomping down flesh and bone right next to you. What if your friend there thinks you’re getting a little too close? They might warn you away by severing your arm”
It is theorised that it might actually have been an advantage to have smaller arms, so there may have been some selective pressure:
https://phys.org/news/2022-04-rex-short-arms-lowered-frenzies.html
In case of larger species with a tremendous bite force getting bitten in the arm would probably result in very bad, and likely very short, times.