Not all of them do --- MIPS was very common once (now probably being replaced by RISC-V), and I've come across recent (<5 years old) lecture slides from Indian universities where they still use the 8086/88, 8051, 8080/8085/Z80, etc.
My university did that switch over in '18. The course originally taught MIPS but shifted to RISC-V, partially though because the book that they taught from was updated from MIPS to RISC-V. I really appreciated the switch, especially as RISC-V becomes more and more relevant.
We use ARM. Because then we can lean on some things (e.g. the ARMlite simulator) UK schools built for A-levels.