Before the craze of cryptocurrencies, bitcoin has been known for it and the idea came out from others and that's when the altcoins were born. Whether there will be alts or none, the crypto market has huge potential even if it's bitcoin alone. Think of how much bitcoin would be if the total market cap is on it.
Nah, the craze for tokens and ICO is what you're talking about. We had alts long before 2017, I came into them in 2016 and they were around since at least 2013, maybe earlier but I'm not aware or if they're still around even. CMC was already crowded when I first looked and this wasn't even counting all the nonlisted coins!