It doesn’t allow Dick from marketing to update the content without having to learn a skill.
Even though wordpress is an unsecure piece of shit, it’s very good at doing a just good enough shitty job quickly and cheaply (most of the time by adding a metric crap ton of even shittier plugins). Hence it’s massive popularity.
Everytime checked someone else’s WP, the only thing that came to mind each time was a Jenga block tower. Bunch of themes and plugins that do god knows what and interact together in mysterious way. Touch anything and there’s a very good chance everything comes crashing down.
I personally send people to Wix, but I guess Squarespace is fine.