Call was playing centerfield all the way through his minor league career. Way.more innings in CF in the high minors than left or right.
Andrew Stevenson also has a preponderance of his minor league innings in CF. He also can't play CF to enough of an MLB standard to make up for the fact that he can't hit.
Call isn't a prospect. He's 28. He is almost certainly what he is going to be. He got DFAed by an organization that was screamingly desperate for a centerfielder.
Lane Thomas is 27. He also played mostly CF in the upper minors.
I see a lot of minor league games, as I live in AA city. A few of the CFs are guys who can play CF very well but have little chance of ever hitting MLB pitching; most are guys who will probably be able to stay on MLB rosters if only they can play CF well enough to be a viable 4th OF; the smallest group is guys who can very likely play CF every day and also look like they will be able to hit MLB pitching enough to play every day.
The reason for this weighting is pretty simple: the guys who can play the position but can't hit aren't worth keeping around long because they won't miraculously learn to hit; the guys who can both play CF and look like they can hit will move very fast (hi, Michael Harris! Oh, Vic, this is where everyone thought you'd be); and the guys who are fringy stay because even marginal improvement in either category gets you (a) a starter who can hit enough to justify a spot either as a good RF or a bad CF a (b) legit 4th OF.
Thomas is (a) if the offense stays, but that doesn't make him a good CF.