Plastic litter boxes literally soak up the smell of sh*t and p*ss over time as bacteria etc inoculates their pores.

Stainless and aluminum offer less of a home to bacteria.

The cheapo stainless litter boxes on Amazon are such poor quality that they rust after a few months.

Also having a seam where it goes from stainless to plastic in order to provide height creates a crevice for filth to aggregate.

A big pot like this could be hosed out and then soaked with baking soda + vinegar.