This is a HUGE factor. You can deploy a website customised to your needs, with almost any look and style imaginable (look at the top rated themes on themeforest for example), without a graphic designer or web developer. I do consulting work installing and setting up Wordpress websites, and I and my clients love it for this reason.
You can get themes for $40-60 that give your site the look of something that would take tens of thousands to develop from scratch.
But it must have been great at something else first, because that wasn't the case years ago - it was obviously better at something else some years ago.
The ease of installation, upgrades, and enhancement (plugin installation) was what made it really stand out. It wasn't always as mature as it is now, but it was always a little bit ahead.
You can find a theme for $45 that will cost $30K to develop from scratch.
You'll find a few plugins that will do exactly what you want that will cost $50k to develop in-house.
WordPress is great because you have things that will cost you $xx,xxx to develop and they are already available for you at a minuscule cost.