Loot boxes are like a random pack of baseball cards that you can only show to other owners of baseball cards, or someone who is baseball-card adjacent.

Some of them are “rare” in the sense that the card printing company refuses to make more, despite it costing them nothing after the initial card is made.

What’s more is that the printing compamy has decades of psycologic practices to use on their card pack purchasers. For Example:

• Casino-esque animations, enticing younger collectors before that aren’t even allowed to gamble legally, in person.
• Rarity manipulation, making things rarer than listed. If they list anything more than 'trust me bro.'
• Making sure that purchasers are surrounded by pack buyers who have already got the rarer cards, generating card envy.
• Removing entire card sets from purchase wirh the whole purpose of making purchasers feel like they will miss out, right now and forever, if they do not buy more packs of cards.

Finally, there is also the fact that all of these cards are entirely digital, so the existance of the cards depend almost entirely on the whims of the printers.