I agree this is a terrible move, but I think it is because black needs to develop queenside. If he could safely castle queenside, the game is won without any effort at all

I disagree slightly. Yes, black's positional structure is garbage, but white's is worse, with the exception of the well placed knights. Black's real problem is that his king is stuck in the middle with a very weak kingside pawn structure. I haven't seen the end of the game yet, but I'll be this is what allows white to win.

Yes, black's tactic should have been to trade the board down as much as possible... not to attack defended minor pieces with his queen

Black has lost a lot of tempo for no reason, and he is no closer to castling out of the knights reach. White's rook's are bursting at the seams to get into the position as well.

I don't think there's anything necessarily wrong with getting more free material. We have all been in situations where a good position will win over more material. BUT, there is a limit to that. If you just take too much of the other person's material off the board, the options eventually slim down to nothing. Chess is a game of finite material. The problem here is that black has negected his king's position the entire game. If he had safely tucked his king away, he could snatch all the material he wanted without fear of retaliation.

Agreed. And his king and queen are both ridiculously positioned. Glancing at the board, you wouldn't even notice that white is down so much material... you would be scared for black.

Exactly. Black was snatching material, which as I said was not a bad idea, and he should have followed up with the mate threat, which white would have had to deal with. Instead he fell back to responding to white's moves, and white gained the attack.

Revealed checks and double checks are the most dangerous weapons in chess. Baker of course uses them well.

Yes, black is still winning, but psychologically, black is scared out of his wits. And white's pieces are menacing.