Because other teams consistently over value the position in the draft. If there's a player they value on the board when their turn to draft comes around im confident they'll take the player.
Their interest in several FA wr's shows that they don't trust the likes of Mellette, Brown or Thompson either. And now that they're looking into a proven vet like Steve Smith you knock it on the basis that it will take reps away from the young receivers that Joe needs to grow with? Seems like a contradiction unless I'm misunderstanding you.
And besides, it doesn't matter where the player was drafted (especially with WR's historically) as long as he can play. I'll take an undrafted Marlon Brown over 90% of the other receivers in his draft class. Besides, it looks to me like we're going to hit on a FS and WR/TE in the 1st 2 rounds of the draft. I think if Mike Evans is there at 17 we take him.
If not I think we'll trade back 5-8 spots and take our pick of Pryor, Clinton-Dix, Ebron, Benjamin, Cooks, Beckham, Lee or whoever else they may value. My gut says it would be Pryor or Clinton-Dix in the 1st if this scenario plays out because of how many talented receivers will still be on the board come the 2nd round where we could use the extra pick(s) to trade up in the 2nd if needed to land the guy they covet. It's very possible that 3-4 WR's will still be around in the 2nd round that in most classes would have 1st round grades.
And just as an added tidbit, our scouts aren't just looking at this year, they're always scouting for future as well. With that in mind, while WR was a position of need last year, it just wouldn't have been sound decision-making to reach on a WR last year early in the draft when you know the following year (this year) you can likely land a much better prospect with a lower draft pick.