There's a huge maintenance burden with WP sites and many things break if you dump them to static files.

Also, the WP plugin ecosystem is almost as "dirty" as mobile apps are - few things are really open source, there's "please give us 5 stars" popups everywhere, fishy data collection, constant uspelling to premium offerings... It's just not a good experience to work with, unless you code most things yourself (in which case you will be absolutely disgusted by most of the API).