[notahacker]

My suspicion is the main reason is that the costs of providing checking account functionality are high (banks subsidise this with penalty fees and marketing loans/mortgages and credit cards to their checking account customers as well as earning significantly higher returns oj their investment portfolio than they pay depositors). As much as in theory I'd love to hold money I might need to spend in the near future in fungible, low-risk government bonds, the middleman provides quite a lot of value in convenience.

Presumably you have put some thought into how you're going to manage these costs (beyond not providing branches) or what checking account functionality you are uninterested in providing.