Not yours, not your problem

If it's not yours, it's not your problem.

This is why you assign ownership. If it's no one's problem, it will never get fixed.

You can bake this in your purchasing process. When approving a new web app, or a new gadget, decide who will be its owner.

This person will be responsible for enforcing information security policies around that system. They will also be the custodian of the information that gets processed and stored on it.

Owners follow security procedures and report about their status on a regular basis.

Assigning ownership allows you to make sure that every issue gets handled. It also makes you think twice before adding more components to your infrastructure.