I can think of a reason: an ETF would allow me to save Bitcoin for retirement with tax benefits. The downside is that I'd have to trust the ETF for several decades and pay fund costs, but (at least where I live) the tax benefits are substantial in the long run.
The idea is not good at start. Bitcoin and cryptocurrency give us control on our coins and tokens with private keys, mnemonic seeds. I could be wrong but I don't feel too many barriers from knowledge to practice in order to create a wallet and store my cryptocurrencies including bitcoin safely.
People who want to use Bitcoin ETFs and other cryptocurrency ETFs will not actually own any coin or token, and if those companies do shady things, those people will gain nothing in their hands eventually. Not only tax but also with a bigger risk, losing all their money to ETFs.