Same reason gold ETFs are big -- people want exposure to the price of gold, but managing physical gold requires effort that many are not willing to put forth.
On a systemic side, ETFs have a number of advantages; notably a credit market (share borrow, etc.) which can lead to effective shorting of the price of the underlying, something that is difficult to pull off without getting suckered in by the next FTX. Plus inclusion in other ETFs, inclusion in various retirement schemes, and generally the wide availability of liquidity in equity markets.
1. Low fees. I think five of the ETF filers even have 0% fees for first 6-12 months. Compare this to Coinbase, where the fees will seem astronomical in comparison (maybe this drives Coinbase fees down.)
2. There is a non-zero number of people in the family office investing world that don't want to deal with learning new tech and just want to call up their stock person on the phone to buy them something.