Any team that wants to trade for Luck must consider the Colts' needs. Making a move with Luck would signal that the Colts believe that they can still compete with Peyton Manning at quarterback.
After going 2-14 without him, it's clear the Colts have multiple holes to fill around Manning. Any team looking to trade draft picks for Luck must understand Indianapolis wants to win now. A third-round draft pick in 2015 isn't going to hold much value for the Colts, they're looking for selections that could net immediate starters, particularly on defense. Knowing that, only teams that send back a top-10 pick or a package of multiple early-rounders need apply.
However, teams with picks later in the first round have another path to Luck. Unlike most teams trading top-five draft picks, Indianapolis would covet veteran players that can start for them right away. That gives good, deep teams a chance to use that depth, along with a couple of draft picks, to make a move for Luck.