Again the Bills had the slot covered with Shakir and Samuel, who was signed before the draft. They needed an outside WR. If they had drafted Ladd, he would have just taken targets away from Shakir left them with a bad at outside WR. The juice wasn't worth the squeeze.
As for BTJr., sure that might have truly been the one who got away, but there were many who felt he was a boom or bust prospect and basically a straight-line runner. The Bills would have had to give up a 3rd rounder at least to get him, assuming there were any trade partners and that was a lot for, again, a boom or bust player.