20 years later, and still nobody's even come close to PHP's ease of deployment
twitter.com
twitter.com
It's also why the likes of Media Wiki (for wikis) and the old guard forum scripts (phpBB/MyBB/SMF/vBulletin/XenForo/IPB) haven't been dethroned in their markets too; using PHP means setting them up is basically trivial compared to competitors in other languages.
So if you're trying to compete with one of these scripts, maybe bite the bullet and just go with PHP like they did. It may not seem as 'cool' as going with a more modern language or tech stack, but it makes your script easy to deploy and gives it a lot more server support too, which likely outweighs those other factors if you're aiming for the wider market.
The thing is: A FastCGI Python script still requires several lines of boilerplate to do the same thing a PHP script can do (i.e. statelessly answering a request). PHP makes that just damned easy.
I wonder if you could achieve those ergonomics with Node/Express: you spin up a daemon and put JS files in a directory that just export HTML render-functions, and bam. People can just "visit" your JS templates.