I'm not sure if I agree with the premise here. Historians on the whole (I can't speak for the sub of course, since I've only been here about a year) certainly havn't ignored geography and ecology - one need only look at the French Annales school of historians (famous for starting more or less every book with a geographical chapter) and the ever-expanding discipline of environmental history. I do think that a problem which does happen, and which historians rightly get annoyed about, are experts from outside the historical profession (not only geographers and biologists, but also geneticists in particular) who act as though they are experts in history, and how make big announcements about how they've 'solved' some historical mystery after only a cursory glance at the literature. Of course, they never do 'solve' the mystery: they either state something that specialists have known for decades, or they've misinterpreted something basic and are totally wrong.

That is why many historians are wary of non-historians or specialists from other disciplines who show up and make sweeping pronouncements about the past. It's an attitude (that's prevalent among the general public too) that history doesn't require any special training or education - it's just reading books and telling stories; sure, any reasonably intelligent person could do it. And that attitude makes them about as credible as I would be walking into an evolutionary biology conference and pronouncing myself an expert since I've read Darwin and Dawkins. So it's not an implicit bias, it's a reaction born out of long experience.

It should be noted however that the above characterisation usually only applies to the most egregious cases. There is a lot of good work being done by climatologists, geographers and geneticists who work with historians, each contributing in their fields of expertise, to advance our knowledge of the past. But unfortunately they tend to get drowned out by the loudmouths, and understandably historians can be suspicious of outside contributions.

From my reading on African history, I think Africanist historians and archaeologists are happy to explore topics like archaeobotany, climate variability, epidemiology, and include those aspects in historical research.

For example, I would point to Emmanuel Akyeampong's book Themes in West Africa's History which includes chapters on disease in West African history, ecology, and holocene pastoralism and climate change. The chapter on ecology was written by James Webb jr

Or I would also point to this french journal article which again explores holocene climate variability and the effects on human settlement patterns.

Or again, Susan McIntosh's chapter which again explores climate variability.

There are entire books written about archaeobotany in africa

So, I wouldn't say that Africanists are hostile to exploring the impact of such factors.

But, I will admit that I have some specific complaints about Jared Diamond specifically. He has been known to make provably false claims about African history.

So, I think perhaps that what you are seeing in those FAQ posts is an expression of the deep suspicion that some folks in this subreddit have of Jared Diamond and his claims of enviromental determinism in Guns, Germs and Steel. Not a bias against all other researchers who would have the "temerity" to comment on African topics.