My complaint about Wordpress is always about how frequently it gets attacked. I have had multiple wordpress websites hacked even after keeping them regularly updated and even after having special "security" plugins such as Wordfence installed, the application firewall installed etc.

It puts too much of a burden on the site owner from a security perspective.

Quite frankly, Wordpress leaks like a sieve. I wish this wasn't true because it is really one of the best/most accessible CMSs around. If they fix the security issues, it would just be wonderful.