Not everybody finances a startup with a mountain of cash. If you're funding your business with your life savings and credit cards, it's difficult to place a premium on a domain name while contemplating how long you can pay your mortgage and put food on the table.
Also, blind optimism is not required for success. And no domain name is an antidote for a shitty idea that nobody cares about.
You are right about the chitty idea, but decent .com names are dropped every day. (You need to scout for names every day though, but will become a nasty habit in no time.) I have found that people, outside of tech, will remember weird, odd .com domains. I got people to remember physibles(and how to spell it.), and these were senior citizens. (I guarantee these people have never been on the mother site either!)
I tried a different domain with a .io domain; and it just wasen't worth it the effort.(they knew about .net. ,org, but that's it.). There's almost a anger that comes up when a domain ext. gets to specific, like .photography?
Also, blind optimism is not required for success. And no domain name is an antidote for a shitty idea that nobody cares about.