Many interesting RNN architectures use things besides what can be done with the “vanilla” RNN/GRU/LSTM - the classic is when one timestep’s output has an impact on the next timestep’s input - one prominent example is attention.
Once you have things like that, you cannot use the multi-timesteps anymore. I guess that people still like them, either because they’re used to them or because they still offer some speed advantage, but fundamentally, most uses are very similar to the *Cell variants.
Best regards
Thomas