The Arm architecture families have evolved over the years to add new features or reach higher performance points. Arm always considers solutions holistically, so that a feature does not compromise another aspect of the family. For example, MVE on Cortex-M55 was carefully architected to consider both raw compute performance and available bus bandwidth and energy envelope. Trying to fit The Armv8-A Scalable Vector Extension (SVE) into a Cortex-M core is not feasible.
Similarly, Trustzone for Cortex-M was designed to retain the key aspects of microcontrollers: power efficiency, simple software stack, and fast context switch. For Cortex-R82, an important goal was to preserve the ability to handle hard real-time tasks while still enabling Linux support.