The purpose is to secure the coin without a central authority.
Bitcoin (proof-of-work) uses mining for the same purpose at huge expense; people need to buy expensive ASICs and burn through massive amounts of electricity running them.
CLAM (proof-of-stake) replaces that with staking. The proposition is "stake your coins to keep up with inflation to help secure the network; if you don't, you'll fall behind".
Your banana example is a good one. The banana manufacturer isn't going to be any more impressed if you come to him with 2 CLAM representing 10% of a 20 CLAM supply than if you offer him 1 CLAM representing 10% of a 10 CLAM supply. If he was then whatever crypto has the biggest supply would be the most valuable (DOGE, maybe).
Because there will always be some who don't know how to stake, or can't be bothered, or who have lost their private keys and so can't stake, staking will inevitably cause your share to grow slightly compared to the people who aren't staking. Of course, with CLAM we also have the "un-dug" CLAMs - millions of piles of 4.6 CLAM just waiting to be dug up by newcomers to the coin.
The problem with all crypto that have been invented so far is that if you don't have them they are not useful and the early adopters and dev have a gargantuan advantage over everyone else.
The millions of piles of 4.6 CLAM is just here to tease and add some more uncertainty to the mix