the idea of locking up coins in a 30, 60, or 90 days already exist in some platform, like in Binance, they offfer rewards associated with it in order for people to take part, and without that, these systems would attract few if any users, thus restricting their potential. It's a transparency that might get added by including some "frozen coins" or "hodler %," but doing so may bring about manipulation or overcomplication. Perhaps better than building a whole new system, improving the existing staking models that manage to provide security and incentive will meet these complaints more adequately.
They offer it to customers to lock for example BNB on Binance exchange for benefits like reduction trading fee, VIP program, and more, but with Bitcoin, do you actually want to take risk by locking your bitcoin on any centralized exchange and take minor benefit but have to accept very big risk?
I guess experienced Bitcoin investors don't want to take this risk, because with collapses and death of centralized exchanges and centralized platforms, they do understand importance of "It's your private key, it's your bitcoin".
Exchange graveyard with different reasons of many exchange deaths, can fear many people.
https://www.cryptowisser.com/exchange-graveyard/