It clumps fine for me. It might be your cat(s) that are causing it.
I know someone that told me her cat digs and scrapes so much she breaks up the clumps.

Maybe try to make the litter deeper in the box. I keep mine only about 1 - 2 inches from the top of the box edge. Of course mine are hooded so I don't have a mess around it.

OH, and one time I had a box of TidyCat and noticed after I got it home that the pull tab was gone. When I opened it I discovered it was NOT TidyCat! Someone filled it with another kind of litter and returned it to the store! So now I check for the pull tab to be intact.