They're trying to follow the BTC steps, perhaps. These altcoins actually got different uses, unique characteristics that they're trying to bring to the masses, sadly not everyone bites it.
They don't really have a different use. As you have said, they're following bitcoin which is a payment for all transactions and the same use. There's no difference between the use of bitcoin and these altcoins. They have a preferred industry to be made as a token but that's just the same as bitcoin being a payment for most transactions. It all started from the ICOs which preferring to the industries that they are promoting like in Energy, precious metals, you name it, there are many of them before.