That is what I've observed too. My impression is that people go to RTOS for libraries and dependency management, which you kinda just get out of the box with Rust, cargo and crates.io.
A lot of applications simply don't use the MPU. And then consider what you get from Rust memory safety and the reduction in overall complexity of the firmware without the RTOS.
One of the things not immediately apparent for people coming to Embassy is that you can mix and match RTIC with the Embassy HALs. So the more appropriate comparison is RTIC vs the Embassy async executors.
A lot of applications simply don't use the MPU. And then consider what you get from Rust memory safety and the reduction in overall complexity of the firmware without the RTOS.