Because AMD gpu division is a much smaller division in an overall larger company. They physically cant push out as much features because of that. When they decide to make a drastic change to its hardware, its rarely seen till its considered old news. Take for example maxwell and pascal. You dont see a performance loss at the start because games would be designed for hardware at the time, in particular whatevers the most popular.

Maxwell and Pascal had a notible trait allowing it to have lower power consumption, the lack of a hardware scheduler as Nvidia moved the scheduler onto the driver. This allowed Nvidia to manually have more control of the gpu pipeline allowing for their gpus to handle smaller pipelines better, compared to AMD which had a hardware based one with multuple pipelines that needed an application to use properly to maximize its performance. It led to Maxwell/Pascal cards to have better performance.... Til it didnt, as devs started to thead games better, and what used to be a good change for power consumption evolved into a cpu overhead problem (something Nvidia still has to this day reletive to AMS). AMDs innovations tend to be more on the hardware side of things which is pretty hard to market because of it.

It was like AMDs marketing for Smart Access Memory (again a feature AMD got to first, and till this day, works slightly better on AMD systems than other ones). It was a feature that was hard to market because there isnt much of a wow factor to them, but is an innovation.