My highly speculative response:
They want to keep additional developmental OL when they draft 4.
Cooley could be on the block or asked to restructure. Cooley is almost 30, we are rebuilding. Let league see he's healthy, trade him before deadline?
They will try to go with 2 TEs and Paul, to free up roster spots for OL and WR.
They see a player with potential who they want to get reps, and there are few at WR.
They have concerns about his speed and separation against CBs. They see him primarily as red zone guy--basically a 2nd TE.
What this would mean if this were a perennial good team like Pats or Steelers: Cooley will be traded next offseason because he is 30 and we are going young. They are planning for that by grooming someone early, and will draft a late round blocking TE next year after trading Cooley, making our TEs: Davis, Paul, Rookie.
The want insurance in case Davis tokes it up, and Cooley is injured.
Better question: if Paul becomes 3rd string TE, WRs are:
Garcon, Morgan, Hankerson, Robinson?, Armstrong, Gaffney, Moss?
The smart play is too get rid of Gaffney, Moss, and Cooley, and go young--though not maybe all this year. If Robinson shows flashes, or Morgan is good, why keep Moss?
Ideally, our WRs would be: Garcon, Morgan, Hankerson, Robinson, Rookie. Assuming Robinson shows something and can replace Moss. This has to be the year you scuttle old guys and let RGIII develop chemistry with guys he can play with next decade.