I actually did come across a thread on this forum some weeks ago, where a user is selling testnet bitcoins, I've tried searching but cant find the thread anymore, and I can't even remember the board it was posted, maybe op would have made use of that if he eagerly needs the testnet bitcoins and don't mind spending a few bucks to get it.
In actual the Testnet bitcoins are worthless, they have no monetary value but still if someone want to purchase it then who can stop that person. I suggest everyone to avoid purchasing of testnet bitcoin because once you purchased it then you won't be able to sell it when you need your money back. I'm very sure that once this airdrop thing gets halted then generous members of this forum will again offer free testnet bitcoins.
Why would anyone purchase testnet bitcoin as an investment?; to later want to sell it back? That's stupid AF if you ask me.
Testnet bitcoin might be worthless in general sense, but those who spend money to buy it actually give it a worth based on how important it is for whatever they want to use it for, and for your information, testnet bitcoins aren't for airdrops purposes alone, developers also use it for testing their products before they make the product live on mainnet.
If I was a developer and building a project that requires testnet bitcoin, and the faucets arent giving me the amount i needed for my testing purposes, and I have the money and have an option of buying, would I rather wait for enternity to get the coins for free, or just spend a few bucks on the amount i want and then continue with my work?
People spend money on what is really important to them when they can't get it for free, doesn't matter whether it has worth or worthless.