The Bears are a lot farther away than one WR, no matter how good he is.
And while Harrison is the clear #1 WR, Harrison/Nabors/Odunze are ranked 2/5/10 overall by PFF so there isn't that big a gap between the three of them, especially if the Bears can garner multiple picks and still get a very good WR. Depending on who they trade with (NE at 3 if they fall in love with one of the top 2 Qbs), they still might get a chance to pick Harrison who likely won't get past Arizona @ #4. Atlanta at #8 might be looking for a qb and they would still give the Bears a shot at one of the top 3 Wrs.
There are probably 6 1st round worthy WRs in the draft and 3-5 more that are 2nd rounders.