I agree with the folks positing that the G-Man put the suit somewhere where Dr. Kleiner could and would recover it (perhaps even influencing Kleiner to do it). This brings up an entirely seperate and seldom-discussed point, however:
Clearly, the G-Man is intended to be the agent of ex machina within the narrative: after all, the whole 'psychedelic tram through netherspace' final speech in HL indicates that the G-Man probably isn't really attached to 'the Government'; at least not what we think of when we say 'the Government', anyway. So who is the G-Man and, perhaps more importantly, who does he work for?
Along those lines, I didn't have a problem for why Gordon was doing the things he was doing in HL2. You're an employee of the G-Man. You have to figure you were awakened to do something. What is there to be done? Fight with the Resistance, or fight against them are about your only two options. (I doubt very seriously you were hauled out of 'sleep' to spend your time making bootleg liquor and smoking home-grown, as much as you may need a vacation.) Since, a) your friends are a part of the Resistance, and b) you were killing aliens before for the G-Man...
Throw on top of that the fact that the G-Man inserted you right where you would encounter Barney and be dragged into the middle of the Resistance, I thought it made perfect sense.