I'm not disagreeing with you, but I don't think it's usually as simple as that for anything useful of non trivial complexity.
Most of the time, more power also brings more complexity. Cortex-M7 mcus, for example, typically can't reach their max CPU throughput without turning on instruction and data caches or "Tightly Coupled Memory". Data caching opens up a whole can of worms when interacting with memory mapped peripherals. Some MCUs with data caches have peripherals glued to them that are fundamentally incompatible with caching, leading to having to use indirect tricks like using DMA transfers to interact with them. TCM partitions your available memory space, leading to arbitrarily complex application specific linker scripts.
Newer chips are sometimes less capable on different axes. It's easier to use a 5V chip to interact with a 5V circuit, rather than a "better" MCU that is only 3.3v tolerant and requires a filtered 1.8V power rail for its internal circuitry. More complex CPUs generally have less predictable and potentially slower interrupt timing too.
Spinning new hardware also isn't cheap like spinning new software is, both in terms of dollars and in externalities. A popular community maintained firmware dropping support for an old but popular hardware generation that's become burdensome to maintain due to incremental feature bloat may be perfectly justified by the volunteer developers, but it does effectively turn that old hardware into e-waste. A company producing widgets with embedded components in it might want to defer the risk and schedule hit of switching to a new MCU architecture for as long as possible, in order to balance overall company goals and limited engineering resources. Justifying engineer months of work "because it's better and everyone will like working on it more!" is a lot tougher to prioritize than "because we only have enough stock left for 6 months and then we're scraping ebay".