Why?
Well, even with the Rams being a high-scoring O, they're not going to have more than, say, four situations a game when they need to worry about endzone matchups. And that's if they don't score from further out, obviously. I'm guessing they'd prefer not to have to set up camp in the redzone to begin with, and just watch Gurley or some one else take it to the house from waaay back, etc.
Okay, so, tops, four times a game. Likely fewer. Draft a receiver with the requisite skill-set. He doesn't have to be "fast." Quick helps. Agile, too. Doesn't need long-speed, though. He should be tall, with long arms, big hands, a serious leaper -- like David Thompson. The whole "catch radius" thingy. He needs to be strong enough to win jump balls consistently. I think a basketball background holds well throughout this list, and the Rams should be checking out all kinds of "off the grid" possibilities.
In short, they don't have to draft a "top wideout" early. They need a specialist. They need a guy who listens to the old-school tape by Bob Johnson, watches it go up in smoke, runs for his life before he's shot by fifty assassins, and makes it to the game on time each Sunday. That's it. I think they can find him in the 6th.