The US is also really dependent on the flow of dollars going through SWIFT. Kicking countries out means alternatives have to come online. If those get too popular it poses a huge threat to the entire US dollar reserve currency system.
It's not kicking countries out, it's just kicking Russia out. It will be a blow for all the Western countries and banks conducting business with Russia, but a necessary one.
It's not just dollars that are flowing via SWIFT. SWIFT is what blockchain wants to be, it's a way for banks to send and receive funds of many currencies.
SWIFT is a messaging system.
The actual transfer of funds is performed with correspondent banks, but they won't perform the transfer if the government says that they cannot have accounts opened by banks from other nations, then that's up to that government, not SWIFT.
SWIFT is being used as "shorthand" to mean that Russian banks will be cut off from the world financial environment. They will have to evade those sanctions via, for example, trading with multiple hops through China, if China allows them to.
