New research suggests T. rex evolved its famously short arms alongside adaptations for an exceptionally powerful bite

[u/Intelligent-Drop7133]

https://www.earth.com/animals/t-rex-traded-its-arms-for-one-of-the-deadliest-bites-in-history/

[u/_Gesterr]

I always assumed similarly, but also that it makes sense because of how predatory theropods are balanced on their hips. A larger and more powerful head would mre weight forward of their hips, meaning they'd be offbalanced without some concessions like an even longer heavier tail, or more efficiently as noted in the article, a reduction in arms to compensate for the heavier jaws.