Do you or have you ever worked in science? I did for a bit and that was not my impression.
I imagine it depends heavily on the field. In some fields there are ideas that one can’t seriously study because they’re considered settled or can’t be studied without doing more harm than any believed good that could be achieved. There are others subject to essentially ideological capture where the barrier to publish is largely determined by how ideologically aligned you are (fields linked to an identity group have a bad habit of being about activism first and accurate observation of reality second).
On my instance you just click “Communities” at the top and it gives you a list of communities with three options at the top Subscribed/Local/All just like the main feed. Click all and you can browse or search the list of all communities, though the search is not great.