Apple seldom updates the Apple TV devices, and when they finally do, the updates are usually just incremental updates.
This isn't exactly correct for all the models. While the ATV doesn't get updated yearly, there does seem to be a pattern, and it is not just incremental.
2007: ATV1 - First generation, very different from the successors.
2010: ATV2 - The first big update. New form, new OS, new features.
2012: ATV3 - On the surface, maybe incremental, but it was equipped with new A chip, fastest at the time, with the exception of the A5X that was launched in the iPad the same day that the ATV3 was launched.
2015: ATV4 - New design, new OS, new features, like the ATV2. Slower A chip than other current HW.
2017: ATV4K1 - Like the ATV3, might seem only a small incremental update, but it launched with the fastest A chip at the time, the A10X. This was a huge upgrade for the GPU as well.
2021 ATV4K2 - This one breaks the cycle in a way, as the A12 has a less powerful GPU as the A10X. The ATV4K2 was the first model that the chip was not a current year chip, and it was a few years old. I suspect this release had more to do with using the same chip as many other devices that was still being sold, as the A10X was only in one other devices, and one that had been discontinued for a while.
202? ATV4k3 - I have a feeling this will go like the ATV3 and ATV4K1, sticking with the trend and putting a very powerful A chip (X, Z, or M variant) in it, and increasing the RAM and Storage to 128GB ro 256GB. Maybe have a cheaper ATV, less gaming-focused for the masses that just want a streaming box, keeping the storage at 32GB, and keeping the A12.
That, or Apple quietly discontinues it....
Apple seems to put their highest-volume SoCs into the ATV. The newest one has an A12,
I think this was the case for most models, but the ATV4K1 was an odd one, as it had the fastest chip at the time, and it was only on one other device, the 2017 iPad Pro.