With risk comes intensity. Some want to prove that they are smarter than everyone else. It makes for mistakes. Ideology may once have been near the top of the list, perhaps in the 1930s and '40s, when people believed in great causes. But by the end of the 20th century, strong beliefs ranked well below a better lifestyle.
Most spies are traitors.
No high-tech James Bond stuff is required. No safes cracked. No miniature cameras. The office copy machine suffices if the secret is on paper. A disk drive at home.