Why do session hijackers sometimes use your accounts to subscribe to porn subreddits or similar websites?

So, a few days ago a friend of mine had their computer compromised by a malware. The attacker hijacked their session tokens and got access to their Gmail and a few other accounts. It wasn't a huge deal since they managed to stop the attack on its tracks, signing out of everything, changing passwords, dealing with the malware, etc.

I can of course understand the motivation behind hijacking email accounts. One thing I don't understand though is that the attacker …

access accounts attacker compromised computer cybersecurity deal gmail hijacked malware managed mine porn session subreddits subscribe tokens websites