What MCCB and MCB are called differently in North America?

Because that is what they are named. There is no standard naming book.

Even your Dictionary is different. You call an Elevator a Lift and  Phone a Telly.

You talk English and we talk American.

There are 4 flavors of English:

British, Canadian, Australian and American.

They are different. So what.

You are confusing intended function with occasional use. A MCCB's function is as a circuit breaker but it can be used when needed as a disconnect switch. I have seldom heard some say, "Go open the main disconnect switch." they usually say, "Go open the main breaker."  They never say, "Go open the MCCB"

A "Disconnect switch" is, I believe, what's known as an "isolator" in the UK; a large switch that disconnects (isolates) all power from whatever it is connected in line with.

eg. Such as the master switch in line with the supply in to a distribution board or consumer unit, or disconnects the power in to a permanently wired machine.

There are also high-current circuit breakers that combine both overload protection and isolation functions, but those are not "miniature" class, they look similar to isolators.

MCBs - Circuit breakers - are overload protection devices; they switch off automatically is a load draws too much current for too long, or (usually) instantly if there is an extreme overload.

Most are thermal-magnetic types, with a heating element to sense and average out minor short-term overloads, and a solenoid coil for instant operation in the case of a higher current fault.

There are also ELCBs, aka GFI or "core balance" trips - Earth leakage / Ground fault circuit breakers, that detect an imbalance in the live/neutral supply and return currents (as caused by a fault to earth) and disconnect the load if that occurs.