Country: Iceland
I think perhaps to understand more we must first understand what Bielsa wants from his CF.
Got to about 3:50 in this video and the narrator starts talking about how he expects his 4 attacking players to be able to rotate positions and fill in for each other in almost a total football style manner. Does Eddie have the attributes to fill in at Wide forward or as a 10? Let's not forget that Bielsa puts huge physical and mental demands on his players, perhaps he feels that Eddie isn't quite ready to cope with all that and he knows Bamford is someone who can trust more. For me it's not just a matter of saying look Eddie is scoring a lot of goals you have to play him when Bielsa has clear demands from his CF which he clearly sees Bamford as more suited for at this particular moment.
Glad some youtuber who knows Bielsa and what he is thinking has clarified that Bielsa wants striker that cant score.