It absolutely can't be replaced by a simple database, saying that makes me question that you truly understand the technology. Here's the important question, who owns the database and how do you know you can trust them?

Would you trust me to manage a database that holds your money? What about someone who's actively opposing you? How about a foreign nation? That's the thing blockchains solve, a decentralized 0-trust way to have an append only ledger, yes a database can be an append only ledger, but it can't be decentralized or 0-trust, that's the important thing here.

Let me give you a very recent example, Steam has been censored, and has had to remove certain games from their catalog, this happened because PayPal and other payment providers forced their hand. This is the sort of problems that arise from having someone own the database, they can dictate what you do or don't. Let me be extra clear, this sort of censorship is essentially impossible in Bitcoin and other cryptocurrencies because no one controls the database.