I personally don't like loot crates - cosmetic or otherwise. They are predatory and exist to take more money out of the player's pockets. Each company handles it a little different and I'll go over what's good and bad about each game's take on it.
- Valve/Bluehole: Free crates. Keys are purchased with money
- Riot: Free Keys and Crates. Both can be purchased with money (via buying 'store credits') separate. Both can be purchased in bulk for a discount.
- Blizzard: free and purchasable crates. No keys. Bulk purchase discount.
- GGG: Purchasable with money (via buying 'store credits'). No keys.
So just on a loot box system, you have a few ways to entice players to spend. Sometimes the game will dispense half of what is needed to claim the loot with the other half behind a paywall. In Valve's case; you're opening items that have market value and can be sold. With TF2; certain crates were worth opening from a monetary gain point of view or 'gamble'. Other companies coax you into buying more than you wanted due to an offering of 'value' and/or they require you to purchase in-game currency in order to buy crates/boxes (at an exchange rate that leaves you with remainder currency).
That aside, there's some other things these companies do in regards to crate-exclusiveness. Riot for example has a crafting currency called "Gemstones". This currency is required to craft exclusive skins. They are obtained rarely from crates - so rare that if you don't buy crates you will simply never obtain those skins... and Riot has been releasing more skins that consume this crafting item (they probably realized the players who would pay hundreds of dollars for crates would stop buying once they got the 1 or 2 skins that could be crafted this way).
You also have time-exclusivity. When OW first had the Olympic games crates; those skins could not be crafted. You could only get it from the box. I remember watching a streamer open boxes until he got his Genji skin and resorted to buying $500 worth of crates to get it. Riot also has event-themed sales on special crates which have a higher chance to have the gemstones I mentioned - a 'buy now or miss the opportunity for this expensive/rare item'.
GGG does something unique with PoE. They have loot boxes that are very low in cost. The boxes have insane value if you buy a few and don't care what you get from them. The crates cost 30 'coins' and regularly award cosmetics that cost 120 coins, 420 coins, 80 coins, etc. The downside is duplicates can't be rolled into a crafting material or sold on a market. What IS interesting is that the crates are time-exclusive and when the crates are retired, the contents are purchasable individually on the store at their regular store value. So while there IS incentive to purchase the crates, there's also the incentive to wait if you don't want to gamble and don't want to miss out on the items all together.
What I do like about GGG and Riot is that their cosmetic store lists (for the most part) every cosmetic in the game at a flat fee. You can simply buy anything you want while knowing what it will cost you, which I have no problem with. It's also interesting that Blizzard did this as well with Heroes of the Storm until they realized how much ****ing money they were making with OW's loot boxes and decided to overhaul HotS and roll out with the same lootbox horse****.
I get that there are people who don't purchase these things and they don't give a **** and to them it's not a big deal. Objectively, these crates make these companies a **** ton of cash - so it IS taking advantage of people regardless. It's pretty scummy in general and I wouldn't feel bad if they were forced to take that **** out; and if they persist, where does it end? Do they infiltrate SP gameplay like we've seen with Shadow of War? Is P2W like SW:BF2 OK? I just find the entire enterprise to be anti-consumer and should be thrown out.