Proof Of keys was meant as way for the Bitcoin community of retaking and exercising control of their bitcoins ( not your keys not your Coins) by simultaneously withdrawing all their Bitcoins every January 3rd of the year from centralized exchanges, third-party bitcoin services and Custodial wallet providers and moving it to private wallets controlled by themselves.
Why should people use non-custodial wallets to store all of their bitcoin?
Why should people prove their ownership on Jan 3rd each year and not on other days?
The activities can only help third party companies to have more proofs on how many bitcoin addresses are still active and they can run analysis on how many bitcoin potentially was lost (from UTXO data).
https://hodlwave.com/No one's suggesting that people should use custodial wallets, its always best to use to use a wallet that you control directly especially when you are holding from a long term perspective.
But the fact is most people do tend to have at least some amount of money on exchanges which they use for trading.
And most newer people always tend to use a centralized ( coinbase for instance) exchange for their first fiat to crypto purchases either for ease of use or because many dont take the time to understand how to use a private wallet, and these people often then never end up withdrawing their money to private wallets.
These were who the primary target was for the proof of keys event( apart from testing the exchanges ), if nothing else it would help people learn how to use private wallets.