Why buy domain names?
Two reasons I can think of are domain speculation and domain parking. Speculation involves buying up domain names which might become popular. For example, if you know that a particular movie is coming out, you could try to buy up the domain name, and when the movie is released, there’s a chance you might get some money from the movie producers who want to secure the domain name. Parking involves buying up a bunch (thousands) of domain names solely for “parking” advertising pages on them. These can include misspelled domain names for big companies. Since there’s a chance someone will input a domain name in their browser by typing it, and that they’ll type the incorrect name, there’s a chance someone will see advertising and an even tinier chance they’ll click on it and make the domain owner some money from advertising revenue.