Because they are different positions. Physically speaking, just because Ronnie is 6' even and 230 pounds, and runs a 4.4, as opposed to 5'11" and 217 pounds and runs a 4.4, that does not make Brown physically dominant over the 300 pound defensive linemen, and 250 pound linebackers that will be attempting to take Brown's head off on every play.
But wide receivers play in a different area. They play in space. They match up one on one with corners who are typically 6' tall even, with between 4.4 and 4.5 speed on average, and who probably weigh an average of 200 pounds. Luckily for these corners, the wide receivers typically average MAYBE 6'1", but more likely only 6'0", with probably 205 or 210 pounds, and also between 4.4 and 4.5 speed. Actually, I'd say that where corners average 4.45 speed, wide receivers probably average 4.50 in the speed factor. And remember, because these are primarily ONE ON ONE matchups (as opposed to being gang tackled by 1000 pounds of flesh), these attributes become very important.
At wide receiver, when you are playing in space, primarily one-on-one (even when it is a zone), usually one defender at a time unless it is a deep ball against the cover 2, when it would be 2 defenders. Having an average of 6 inches of height over the corners is huge. It's the entire reason 6'4" and 6'5" wide receivers get drafted and are able to make their way in the league despite consistently having sub-standard speed. But, Matt Jones, the freak of nature, has above-standard speed to go along with the 6 inches of height and 30 pounds of weight that he holds over the one-on-one matchups he will face.
Immediately, before he learns step 1 of his technique, defenses will have to double team him by playing a safety long and a corner short. Why? Place a big huge corner or safety (slow defender) on him to keep up with him in bulk and he will beat him deep 10 times out of 10 on a simple fly route (run straight forward, look for the ball, catch it). Place a quick corner on him who is most likely small, and Jones will dominate him physically (ever play basketball against a guy 7 inches taller than you and try to defend him?). This is even BEFORE Jones learns any technique. So what you'll need, is a bigger corner covering him short, and a faster safety covering his deep routes...a classic cover two like we use to play before Saban came to town.
What that also means is, before you've even taught Jones a single thing about being a wide receiver, he has already done more than his share to open up the running game, and your tight end.
