Back in the day or at least when I ran my own bitcoin node, any call against the blockchain was free. This sounds like someone charging for hitting the API on a rented node, as opposed to an actual cost imposed by the currency to consult the blockchain (?) But maybe the contract-generators aren't even running their own node, just piggybacking on someone else's API. Sure. Cheaper.
AFAIU, smart contracts on the ethereum VM can be arbitrarily complex, so you pay the network to execute them, or a random user with an infinite loop would bring down the network.
You are indeed renting a machine to run some code, and if you want many people to use your code you want to make it cheap. There's a trade off.
You can fuck up things on the BTC blockchain too, "burning" crypto by sending it to a dead address has been a thing for a long time.
It always seemed stupid to me that it was possible, compared to sending money to an invalid IBAN, but I'm not a crypto enthusiast so I may be biased.
On BTC, you could send things to the wrong address, yes. But you can't send the wrong type of currency or send it to a nonexistent address. In this case it seems like the contract has created the black hole (not the Ethereum blockchain itself), but that's even more absurd since someone ultimately should have control over everything that was put into the contract, regardless of the source.
Sending currency to non-existant addresses is how people encode arbitary data on the bitcoin blockchain, so definitely possible.
Giving a person control over the funds allocated to their smart contract probably opens holes where they can steal the smart contract's money, though obviously creating software that handles money and can't be updated is its own kettle of fish.
