You should do a deep dive into the normies (not high wealth) who are purchasing the ETF.  I would guess most of the money so far has come from the self employed who have an IRA or people who have left a job and rolled over their 401k into a self directed IRA .  A small subset of people.  The big ETF inflows will be when company sponsored 401k's let the ETF in as an offering.  That will unlock $7.5T in potential ETF buyers and there are tons of working young people who would send it and dedicate 100% to BTC!

To Self custody for IRA holders.  If not of retirement age, it would require:
- Taking an early withdrawal penalty (10%)
- Paying Income Tax (30%)
- Purchasing Spot
- Paying Capital Gains at sale (15% of gains)

For people of retirement age the cost to custody is the same as above minus the 10% early withdrawal penalty.  

I would love to have nothing but self custody BTC, but the ETF is a great option for retirement money that is locked up.