Why WordPress? The User Perspective

In the spirit of constructive criticism, let me suggest these may not be quite the best reasons for “why WordPress.”
1. Every open source CMS comes with essentially the same freedoms, and most users will never exercise the freedoms that distinguish open source from proprietary software. Unfortunately this makes them think these freedoms aren’t very important. To those people I would stress that they need to realize how much they benefit from the people who do exercise those freedoms to make the WP core, plugins, themes, and services.
2. Being able to run in almost any server environment is a very two-edged sword. What this often means in practice is the new user getting just enough rope to hang themselves. A cheap shared server not optimized for WP and using obsolete versions of PHP may be really accessible to the widest possible users, but if at all possible they’d be better off with something more reliable, secure, and efficient — definitely if they value their site, it should show in what they pay for their hosting. I would say it’s more valuable that WP is easy to install, and with the better hosts it comes pre-installed because it’s the only application they exist to host. So let me add to your support for WPengine!
3. The age of an open source project is not nearly as important as the number of versions released in that time — especially over the last 6-12 months from the present. An established project that has frequent new releases may be the best combination of traits. Given WP’s frequent releases, their quality, and the ability to be make upgrades “automagically” without breaking things — and to do this for years — I would say the the unique selling proposition for WordPress from a user/owner perspective is its sustained quality and progressive improvement that still supports a low long-term cost of ownership since backward compatibility is also a priority.