[D] Why aren't new LLMs using the Perceiver architecture?

Perceiver and PerceiverIO (https://arxiv.org/abs/2107.14795) appear to offer significantly improved FLOP efficiency, but new LLMs (including Deepmind's own Gopher) don't use it.

What gives? Is it still too new, or is the Perceiver architecture not appropriate for LLMs?

architecture llms machinelearning perceiver