To get one tent to your last stage before attempting the summit, 70 tents are brought (or so I understand). First base your tents are full of other tents, oxygen bottles etc to get you to the next base. That one has fewer tents holding fewer supplies. After a handful of iterations, you've spread $100000 of gear over the mountain so you can have that one chance at a summit.

The mountain is huge, but it adds up.