Well, there are over 78 million COM domain names taken. And there are only about 100,000 words in a big English dictionary. So, the other 77.9 million domains are made up words and combination words -- including dashes and digits.

As far what tools people used to register find all those domains, you have to keep in mind that people have been registering domains for 25 years. In that time, plenty of tools were written to find the best domain names.

I've wrote a quick tool recently to check the available domains against an English dictionary, without about 100,000 words. Of those, only 1500 were not registered, which are in this list.

The HotNameList website, for example, searches for combinations of words that are common in normal English text, and then checks to see if the domain is available and valuable, using various automated tools.

Plenty of folks have written similar tools.