[quote name='lowdown' timestamp='1478766723' post='3171418']
I see this written quite a lot on Basschat (not really aimed at you Tim).
Why are Keyboard players in covers bands playing Bass lines?
[/quote]
Because keyboard players can easily play two parts at once, so when they play alone it makes sense for the left hand to be providing the bass part.
(I used to play a lot of piano myself, and this is of course exactly what I did.)
The tricky part is convincing them that things are different in a band situation, and that they should stop doing this.
Add to that the fact (fact? claim? opinion?) that many keyboard players are frighteningly arrogant and disinclined to listen to other musicians, and you can see why so many musicians dislike playing with keyboard warriors.