Blocking access at domain root level, but not other pages?

I'm researching a competitor who does affiliate marketing. I notice that their root domain page (say www.abc-website-examplee.com NOT REAL FYI) access doesn't render or show anything, but when you visit other pages with url params (like www.abc-website-examplee.com/c/gibberish?a=123&b=890), then it reveals a webpage.

Does anyone understand what's going on or what kind of technique this is? ALSO: from my research, it looks like the person is scooping up other domains that used to be in business and doing this (blocking the root domain)