Because Monzo very publicly got told by US regulators that it wasn’t going to get a banking licence
The thing is, that’s not their only way to get a US banking license. They could also do as another challenger bank in the US did and buy an existing bank. Pick a small local bank with only one or a few branches, buy it up, apply to “take over” their license, and while it won’t be instant, it will be easier than applying on their own.
EDIT: The only issue I can see here is that drawing down that one physical branch might cause their existing customers to be quite unhappy. So Monzo would probably be stuck operating that for a while until they can get people transitioned over to app-only banking.
And to everyone else, yes, cheques are very much still a thing in America. This is such a problem that there are entire businesses (Plastiq being the biggest) that will take your card details and write a cheque to most non-card-accepting merchants in exchange for you bearing the card processing fee. Many government agencies, state and federal, will only take cheque (or money order), the first two times in my adult life an airline damaged my bag I was told cheque would be the easiest way to be compensated because corporate policy allowed customer service agents to directly issue compensation cheques up to a certain amount but bank transfers of any amount had to be manually reviewed and approved by the airline’s accounting department, to name a couple of things.
Also, it costs small businesses less to issue cheques than bank transfers. For example, in the States I’ve got an LLC (sole trader with limited liability) and my business banking is with Chase. If I want to pay vendors, contractors, etc, I can order cheques from somewhere like Costco and cost of payments would be 6 cents each (the smallest order of business cheques is $36 for 600). If I want to send bank transfers, Chase charges a basic fee of $25/month for 25 payments, resulting in a cost of $1 per payment for the first 25 and 25 cents per payment thereafter. Some other banks don’t even have the ability to let small businesses send bank transfers, requiring you to turn to a third party to process the transfer. Wise works for this but their variable fees for same-country transfers really add up.
And there’s Revolut Business as an alternative but they hold up a lot more transactions for “compliance” and ask for information that a lot of US businesses are absolutely unused to being asked by their bank for payments.
(please bring Monzo Business to the US)
EDIT: Also, as an American it’s really funny to see people talking about Chase savings and rate-chasers in the same breath, because over here, Chase tried to sell me on opening up a savings account for my business with an interest rate of 0.05%. They aren’t even trying here.