The search to improve a team's quarterback room never ends. The demand is great, but a limited supply of quality signal-callers forces organizations to consider every available option.
The quarterback market should be mostly settled from now to the NFL draft. More moves should be expected before the start of the regular season, though.
An injury or an inability to acquire a preferred prospect will usually be the main reason to sign a QB after the draft.
At this juncture, quality starters aren't available. Reliable veterans are. And then there are the wild cards, Johnny Manziel and Colin Kaepernick.