Such trading volumes, which are shown by different cryrtodata aggregators, is a completely normal phenomenon. This is due to the set of different trading platforms in the volume calculation system and filters both in CMC and coingecko, which take into account the overestimation of trading volumes that are usual for exchanges.
In this case, I would be guided by smaller numbers, especially since they are of the same order, which means they roughly show the same thing.
I have to say the main reason could be that as far as I can remember Biswap was also the first place that BFG got listed. This is why anyone who wanted to trade BFG ended up trading it on there and it really helped them get famous as well, biswap was doing fine beforehand but BFG really helped them as well. So, biswap having the greatest BFG volume is not something shocking, anyone wanted to started here and didn't see a reason to move anywhere else.
If there was a case for someone to actually have a reason to move, then I would get it but check all the other places and you will soon realize that there is nothing that makes you end up changing your place, no other place has any sudden advantage, so people are staying there.