As far as I understood, an ETF would allow people (well, hedge funds) to trade in Bitcoin and other crypto without the need to actually hold them? Given the current state of ownership (private keys and a high possibility of fraud or accidental loss), it would be unwise to have a fund invest in a few millions of dollars only to have the security of a Ledger with no way of assuring only restricted and qualified access to the 'physical' tokens.
Also, if there was an influx of fund money, wouldn't it do a lot to stabilise the crypto economy? Not great for someone who wants to Lambo in a few months, but it is essential for long term stable growth and adoption.
Now, I may not have understood what the purpose and consequences of an ETF are, seeing as that is not my field of expertise!