This was not nostalgia either : the reason for doing that is because I was writing webapps for my pinephone. Toying with the phone, I decided I wanted my apps to be webapps rather than GTK apps, so that I can access them either from mobile or laptop (through local network), but I didn't want to have the apps running all the time, in order for them to consume less energy (which directly translates to battery lifetime on a mobile). Turns out that CGI is perfect for that : the only process always running are nginx and fcgiwrap, then all my apps are started only on demand, for the lifetime of the request.
I did expect a big performance hit, but I was surprised it was not so bad. I guess that's because they are C app rather than written in languages which require loading an interpreter before running anything. One app that I rewrote from libmicrohttpd had actually better perfs (although it was the first time I used libmicrohttpd, so it was probably something I didn't do correctly).