first of all, every coin ever released has been a crap coin until it has been proven otherwise. There are still plenty of people in the world who would say they are ALL crap coins.
Now, as to why anyone would mine such a thing... Well, there can still be profit involved regardless of the outcome or determination that any coin is crap or not crap. There is a lifecycle for all coins that often times includes hype. The trick is to find coins with obvious hype and to capitalize on that... at least to some degree. If you really believe in the coin you might hodl all of it until it is a value of your choosing.
I know a guy who always said bitcoin would be $10,000 before he sold it. You can imagine all the rofl he got from people... right up until 2017 hehehehe. Yeah, that guy is pretty rich right now and I'm like telling this guy, "I'll follow you anywhere!" lol
And I will also add that any coin I choose to advertise in my signature is going to live far beyond the usual hype cycle.
I wouldn't say every new coin is a crap coin by default. There are new coins that bring a good idea or good use that are unproven but the true shitcoins are the ones that really solve zero purpose other than a glorified pump and dump. I'm talking the ones that are more concerned with getting listed on an exchange than developing their profit. Then there are coins like this:
http://phoenixcoin.org/ I mean look at their website. What sort of value could this coin actually provide? Yet its still mined and traded!
Also your story about the guy who said bitcoin would have to be 10k before he sold it makes me laugh. Reminds me of when I sold a bunch at 10k and then felt like a sucker when it went to 20k. Now I'm happy I sold it when I did haha