In the real world, people play trading card games all the time and a big part of the ecosystem is trading the trading cards. Only, it is really annoying to have to ship around and maintain physical cards, and I want my card collection in the cloud. Some people would thereby prefer to play an online version of, say, Magic: The Gathering, or whatever the Pokémon one is called, etc.
The problem now is... how do you do the trading part? You could go to the trouble of yourself building a marketplace for the cards and then integrating all of the payment methods required, and then dealing with all of the trust and fraud issues that result from people sending money via banks or PayPal that they later chargeback or refund, all while dealing with whatever crazy tax implications come up from running a market.
But you don't want to do any of that: you want to code a game, and it isn't like Wizards of the Coast is trying to take money off of the aftermarket! They just make money by selling the initial randomized official card packs. Because you went digital now you are doing a ton of extra work and are wasting a ton of time dealing with payment processing issues when none of that is related to your actual business model or product design.
And, at the end of the day, doing that giant marketplace is a hard job that other companies specialize in. If I told you eBay provided some kind of digital asset API that let you simply assign tracking numbers to products but then eBay kept track of the ownership as it changed and all your game had to do is ask "what cards does this user still own?" when it opens, I imagine a ton of developers would jump on that bandwagon.
Only, eBay doesn't provide that API, and likely would avoid doing so out of concern you would shut down the game on a whim and cause them issues; and, even if they did, now your entire game backend would then be built around a single marketplace that might randomly pull your game for some reason and shut down your entire company in a way where you are SCREWED as your end-to-end ownership pipeline is modeled inside of eBay's database rather than being something you control and can migrate.
If only there were some off-the-shelf technology for tracking digital assets that you could trivially add as a dependency to your project, letting you write a few lines of code to define your asset and which had APIs for querying ownership... one which was an open ecosystem controlled by a shared protocol instead of a single company, thereby allowing not just one market but any number of competing markets with different ideas on auctions or escrow to exist. Wouldn't that be amazing?!
Well: that's Ethereum; like, that's precisely what Ethereum is doing. If you think collectible trading card games aren't a dumb idea--and even if you hate them and think the premise is bad for gaming, I am going to remind you that these things are SUPER POPULAR and so your opinion doesn't in some sense matter here as you are just ignoring reality--then Ethereum is a GLORIOUS idea that makes it absolutely trivial for game developers to build them and for users to participate.