Sorry, but for all intents and purposes, WPEngine IS WordPress.
Running WordPress is such a pile of security and customer support suck that nobody wants to deal with it. Consequently, if you are being made to run WordPress, you also want to pay somebody to make the pain go away. If I pay WPEngine, I can tell my marketing and design teams "Customer support is over there. Talk to WPEngine and leave me alone."
If WordPress made their software such that hosting administration wasn't such a fiasco, WPEngine would have viable competitors and wouldn't be able to extract the ecosystem.
Running WordPress is such a pile of security and customer support suck that nobody wants to deal with it. Consequently, if you are being made to run WordPress, you also want to pay somebody to make the pain go away. If I pay WPEngine, I can tell my marketing and design teams "Customer support is over there. Talk to WPEngine and leave me alone."
If WordPress made their software such that hosting administration wasn't such a fiasco, WPEngine would have viable competitors and wouldn't be able to extract the ecosystem.