Weebly, Wix, and Square replace low-end 'web designers' who will usually build atop a WordPress core and stick it on a shared webhost, leaving it to be hacked due to security vulnerabilities. Sure, they leave you semi-dependent on a given web service. But, to the site owner, they're generally dependent on a single developer anyway since that dev doesn't usually give them the FTP credentials.

Weebly is pretty solid and the only major one that's free to use with your own domain. It just has a small 'powered by weebly' at the bottom. And it generates standard HTML and CSS that you can then move to another webhost later if you want. It also does an htaccess for redirects if you're moving from a previous host using different tech. The only downside is that you don't get full control over the URLs.