I'd also add that the rise of cloud computing hasn't helped either. WP was great when hosting consisted of shared LAMP services or hosting your own. But WP is a huge pain in the arse to host on services like AWS (as well as expensive too). So lots of companies that might have opted for a CMS solution like WP could easily be swayed to another alternative. While this wouldn't be the biggest contributing factor -- it's a drop in the ocean compared to the points you've raised -- it is yet another example of how the industry is moving on from WP style content.
I'd also add that the rise of cloud computing hasn't helped either. WP was great when hosting consisted of shared LAMP services or hosting your own. But WP is a huge pain in the arse to host on services like AWS (as well as expensive too). So lots of companies that might have opted for a CMS solution like WP could easily be swayed to another alternative. While this wouldn't be the biggest contributing factor -- it's a drop in the ocean compared to the points you've raised -- it is yet another example of how the industry is moving on from WP style content.