Altcoins being used mostly for speculation purpose. The fact that if altcoin is also having another usefulness like give native coin user a cheap way to send their money. I remind you how expensive the bitcoin and ethereum transactions are. That's why altcoin gives alternative way for people to send or receive their money with lesser fees compared used native blockchain like bitcoin or ethereum.
They're all experimental grounds meant to test the Blockchain's capabilities/limitations. Without them, BTC would've been full of issues by now. I know BTC maximalists prefer to have only one Blockchain, but this simply can't be done. Especially when you need to meet the demands of everyday users. If you scale BTC to the masses, it would become extremely-centralized.
That's where altcoins come in. They're cheap, fast, and full of new and untested features. Most people don't care about the tech, as they're only focused on the profits. While altcoins bring huge profit opportunities, they can also go all the way down the drain in an instant. With BTC, there's less risk involved. Crypto is just getting started, so expect to see more altcoins emerge in the future. Just my thoughts
