If you're helping a client or company build a new site/app, and they are not ready and willing to either maintain the site themselves, or pay for a decent maintenance contract, or otherwise guarantee that security patches and hot fixes are applied in a timely manner, they don't yet value their website/app enough. It's your job—as someone who knows the consequences—to convince people of this.
This applies all the more when a project is built on a widely-used platform like Drupal, Wordpress, RoR, Django, etc. Though bespoke/lesser-used frameworks may provide a tiny amount of protection through obscurity, that's still no excuse for not educating people on the importance of maintenance in any software project.