Netlify CMS and Ghost can feed an SSG but both require a difficult setup for the average user.
WP is complicated too but there are many services that install it for you so you can just pick a theme and start writing.
Medium is probably the easiest to use but... well it's Medium. Super bloated website with annoying popups and a company with questionable morals.
Disclaimer: I'm building a blogging platform so I'm probably biased.
Most WP site owners are average Joes and Janes. Probably 95% of them. They get a ‘dev’ (college kid) to help them here and there, but most are being ‘run’ by complete amateurs.
On the other hand, SSGs are a hot mess. You have to know ‘deployments’ and ‘libraries’ and how to break down your site into partials and a ton more.
And that assumes you are familiar with CLI, the O/S, and sometimes various ‘template’ languages.
Go read the “first blog post” tutorials by any SSG. No mere mortal stands a chance.
If I see one more “so easy! First type ‘npm install yummy-blog -ldx’ and then clone my repo theme into your blah blah blah’.... uh, what? Do you think your kid’s fourth grade teacher has a chance?
But they can sign up for a free WP.com account and post something in 10 minutes. Or if they are slightly more techie and know how to buy a domain and setup a hosting account, they will have a “one-click install”.
WP will (eventually) be “performant enough” as PHP advances and they ditch legacy code. Even a lot of more techie websites and companies use it when they have the ability to use SSGs because it’s just rarely worth the hassle for the trade-off in performance. Inevitably, even those companies want Tina in Marketing to write posts and if she saw a code editor or a command line she’d quit. (And not being sexist - could just as well be Dylan in Accounting who needs to post about his company’s ‘transparent’ finances to show how hip the company is with their 27 employees.
SSGs might never take off. Even ‘easy’ ones that can have a web-based login or ones like Publii have a very limited audience.
What amazes me is that... people keep building more! StaticGen must list 100+. And it seems ne’er a month goes by on HN where some lonely dev doesn’t announce they are building yet another one.
I personally don’t get it. The new ones have all the same friction and nothing innovative over the existing market of SSGs. And no, using Rust or Go to speed up build times by 12 seconds doesn’t count.
The problem is not really that PHP is not fast enough IMO but it's a matter of cost.
Most performance issues can be alleviated with a CDN and a cache plugin. Regular people will not know how to set up those but (I think) WPEngine, Wordpress.com, etc, do that for you but those services are not cheap.
Even if you get the same performance in WP as a SSG the cost will always be superior.
I think SSGs would only take off if it's shown that there's a drastic monetary savings.
