Earlier thread on a similar topic (coming from the same OP, incidentally): why do astronaut audio transmissions from orbit still sound so bad?
My guess is the same as it was in the other thread: The certified technology is rather old but tried and tested, and getting new technology with higher bandwidth tested and certified for spaceflight is an arduous process. The main purpose of Perseverance is taking and analysing geological samples, and the bandwidth is sufficient for that; the images are a by-product, and it’s not worth jeopardising the main mission by installing higher-bandwidth but untested communications technology for a video feed.