1. There is no easier way to set up a standard marketing/business website, despite many quality attempts to build replacements. The plugin library is a big part of this.
2. It's extremely easy for anyone to start hacking on, leading to lots of developers "cutting their teeth" on WordPress by following online tutorials. Show me a self-taught front-end developer and I'll be shocked if they didn't learn on a WordPress site. This has good & bad aspects, of course.
Comparing wordpress and developers, is a bit like comparing how many people like tyres (everybody got some on their car) to how many people enjoy making tyres for a living (not a very common activity).
It's a testament to how being non-technical friendly leads to market success.