The question really is: why open a HSA account anywhere other than with a financial institution?
Long has the employer health insurance market controlled where HSA accounts are held. However HSAs have been around long enough and plenty of assets are held by them and certainly an employee or two has left their employer with an HSA balance for a shift to occur.
The challenge for most is:
1) They do not know where to open a HSA account
2) They do not really understand their HSA account is portable
3) They do not know they can hold multiple HSA accounts
Having access to and knowledge of our options as it relates to HSA accounts can only truly be maximized if every financial institution offers HSA accounts. More importantly, an HSA account which includes an experience they would expect by today's standards.