You could probably build a competing CMS in, say Laravel 4, replace the plugin system with Composer packages or something similar, use Twig and PDO out of the box, and have a much more elegant and modern system that probably almost no one would use, unless the user experience was just as brainless as it is with Wordpress.
Which is also one reason why, I think, despite all the arguments in their favor, static site generators (which do get mentioned now and then as an alternative to WP) still have a while to go before they're ready for mainstream use. It's not enough that it's well coded, it has to be easy too, and easy wins out over pretty every time.
WordPress is being pushed only because the majority of web developers can tinker with PHP only.
I think you're forgetting that most of the people who use Wordpress aren't web developers at all, and most of the 'web developers' who use Wordpress probably can't code much, either, because they won't need to. The ease of the Wordpress install is something they advertise. Once you ever have to touch the code, yes, it's a nightmare, even if you're inured to the horrors of php code. Most 'web development' jobs with Wordpress involve the install, setting up themes, maybe editing the css and installing plugins (because even that is still more arcane than some non-technical bloggers and people want to deal with.)
The "low bar for entry" for PHP comes up as an epithet now and again, but if you're trying to increase the adoption of your particular language, having an application the plebs can run isn't necessarily a bad thing. Does anything similar exist in the Python or Ruby worlds yet, for which someone wouldn't be expected to know how to use a terminal, or handle git?
It is, I think, almost entirely down to being less of a hassle than anything else out there, and especially less of a hassle than anything not written in PHP. Call it laziness if you will, and I wouldn't entirely disagree with you.
PHP is like Perl blended with C and a whole lot of confusion.
Frameworks have made it "better" like ketchup improves the quality of prison food, but it's still terrible on the whole.