Why is the art getting worst?

I choked-

it sounds so aggressive but not aggressive at the same time

it's not, it is a style change to reflect the emotions. Things are less complex, simple and squishy, so the characters themselves reflect that in the art.

Sometimes a series’ art style gets more ... simple over time, usually less complex backgrounds and less details for hair and face shapes. It’s disappointing sometimes if a story’s art starts out bold and heavily lined but becomes less styled over time. I actually like how he looks now, gives him a more expressive look.

Then why don’t fix it yourself the Arthur is trying their best

Pay me