For clients and writing actual content nothing beats Wordpress. The editor is great and a lot of people have used it before so, from a developer point of view, I believe that with Wordpress you should give people what they want. The alternative of demanding they use some 'better' CMS means that the content never gets written or updated.

However, not to disrespect the work that has gone into Wordpress, how hard can it be to write something better for the frontend and get marketplace adoption?

I do not like the frontend 'coding standards' and mess of plugins. Starting straight from the raw wp_ mySQL tables is a less insurmountable task than hacking some theme and bloating it out with 'jQuery' plugins that should never have been plugins. It seems that it is the ecosystem of design agencies with their lorem-ipsum big-up-front-designs and allegedly 'agile' workflows that have made Wordpress into something I do not like working with. Particularly when the add-ins make the backend far removed from sensible, making it a nightmare CMS for clients.

Hasn't anyone written a decent frontend for it that is not a tacky theme with ten thousand lines of CSS of which 97% is not used and a megabyte of scripts to get the carousel and share links working?