Now forgive me for being curt, Frocto darling, but thats pretty much very wrong logic. Obviously Valve wants players to play more, but I don't think the current system actually does that (outside of stats inflated by idling). What Valve is doing is hampering the ability for players to explore content. I don't think I met anyone who legitimately enjoys the unlock system or weapon unlock system. You lock players out of content that they might have fun with! With every patch you're going to get people grinding for achievements and other people who just say 'fuck it, I'm not going to get the items anyways so why bother".
The logic behind random drops has some basis in fact but it is poorly executed. Irregular rewards is a very effective 'hook' for people, but Valve misses it on a number of fronts.
A) It's non-interactive. A slot machine is an action. You pull a lever. You get a satisfying clunk. Things spin. You see all the things you could win. You get...... nothing. Or maybe you get something, and other times you get more then something. You maybe JACKPOT. Random drops miss this completely. Just randomly you get told "YOU GOT A PIECE OF JUNK!" ... hooray? Maybe you wanted it, maybe you didn't. You didn't get the whole build up or excitement or anticipation related to irregular rewards. You just got a prompt.
This is actually why idling is so popular. coming back, knowing you're about to get a ton of stuff, then shuffling through it for the possibility of gold is the type of reward mechanism that people enjoy. It's like random facebook games where you get to play a game of chance every day. Same mechanic. Reliable, player induced and, sadly, exciting. The Idlers get more excitement then the legit players.
B) The rewards are too limited for prolonged enjoyment. Most players have every weapon they want at this point. The system then shows you an item you don't even care about. It's just going to be junked for scrap. The system might as well just hand out scrap, though the act of combining is something I guess. But really, the reward system runs out of steam FAST.
C) Your rewards are almost impossibly far off for casual players. Okay you got the items you want, so now you want a hat. 80 items later. Thats not a goal most people think they can work toward and even then, the chances of them getting what they want are very limited (or take over 100 items).
D) It causes players to feel cheated and excluded. MMORPGs have two types of rewards for this very reason. Reliable (XP) and Random(drops). Reliable rewards keeps the player interested and lets him feel like he's progressing. Random drops are just an extra, almost scandelous extra to excite them. TF lacks that. Theres nothing you can feel you're 'working toward' outside of achievements and those mostly rely on luck too. If you give a player all the content up front, he's encouraged to explore all of it, instead of potentially giving up before all of it becomes available to him.
The system is basically totally garbage. Clearly they intended to do more with it until resources were removed from the team. It's half baked. Ideas like item levels and crafting and a backpack of equipment (even though theres no technical reason to need one) all hint at a larger system they backed away from at some point. The system doesn't even reward you for PLAYING necessarily. It's really just a failure and the only reason it exists HAS to be because somewhere down the line, Valve aborted an even larger potential change to the game (true RPGness?).
Man, Stush basically gave the tl:dr version of my post. Being able to play with toys is fun. Let people play with toys. If you want to also use psychological tricks to encourage people to do boring things but play more, at least limit it to cosmetics and even then, make a system that would be more successful at it rather then just being a joke.