That's because you are using a VIBRATORY tumbler which is made for "kitty litter" tumbling and not ceramic.
...But, I have seen new brass.....at the manufacturers plant & I've even bought some before.
As far as media life, walnut or corncob, I wash mine about once a year & strain thru a sieve. Drys in a couple days.
Been using the same batch, plus about one cup fresh added each year to makeup lost volume during shakeout & annual washing.
For pre-treatment, I soak in a weak acid solution instead of plain water/soap...this removes much of the inside case fouling.
Ceramic media will work, wet or dry, in a vibratory cleaners as well....I've seen them in use at many manufacturing plants...even ammunition manufacturers.
Bottom line, both methods work.
Slim