tatami, counter for tatami mats, fold, shut up, do away with
疊 centers on layering and stacking, like tatami mats placed one on top of another. The ideas of folding, shutting up, and doing away with something all extend from piling or compressing layers together.
疊 is the traditional form of 畳. It combines 畾 (a tripled field, suggesting layers) with 冝 (a component associated with fitting or placing), together conveying the idea of stacking or piling up.
The top 畾 looks like three fields stacked on top of each other, and the bottom 冝 suggests something being placed underneath. Picture tatami mats being layered one by one, then folded and put away.
For ジョウ, imagine a tatami showroom where mats are stacked high: show -> ジョウ, and the layered mats fill the room.