It’s a very limited database that is very slow and scales poorly.
Good luck convincing people that every time they logging into their account or literally do any action will cost them some fees. Refreshed the page? Oops that'll cost ya!
And then eventually that cache will be a database.
And then eventually that database will have some additional data.
And then eventually we will back to where we are today.
Other blockchains make decentralization tradeoffs to process more transactions on-chain per second. For example, Ethereum requires better hardware: larger storage, better CPU and more memory. Solana makes even larger tradeoffs: expensive server hardware costing up to $25000, making it pretty much a central service controlled by the few.
The key innovation of Bitcoin is the decentralization; almost anyone can participate and no one can control it. Sacrificing this for negligble is not worth it. Especially since there are smarter ways to scale the system. Even if you could improve throughput by 100x by making the system slightly less decentralized you would still not reach VISA levels of TPS.
The correct way to scale these systems is using off-chain solutions like the Lightning Network. This way you can process millions of transactions per second.