I can think of a few reasons:
I posted this elsewhere in this thread but I need it to answer your question:
Quote
If Alex Van Pelt (the Browns' OC) is to be believed, OBJ is a complete WR - including blocking.
From this article: [
touchdownwire.usatoday.com]
The other stuff that he does and in the run game, I know it is not sexy, but he is really effective and he really came down and really put the wood on a couple of those safeties in the game. He does a lot of great things other than catching the ball on the field ...And this, from the same article:
Beckham’s coaches and teammates in Cleveland also praised his effort as a run-blocker ...
So there's the first thing: OBJ appears to be a more complete WR that DJax and therefore seems to be a better fit in the Rams bread-and-butter 11 personnel.
Another thing: it seems that DJax either didn't understand his role when he signed, or learned not to like it somewhere along the line. Maybe that happens with OBJ but I have faith that OBJ will toe the line for 8 games plus playoffs, especially when he had other options (including other roles) elsewhere. e.g., he likely would have been the #1 receiver with NE yet he chose LA.
Finally - and probably the biggest reason: money. OBJ gets $3M in incentives if the Rams win the Super Bowl. And then he's a free agent after the season. He has to know that his price tag goes up if he's a productive member of the Rams.
AlbaNY_Ram