The latest pihole updates added the ability to use different blocking technics(NXDOMAIN or NULL) which don't rely on an answering webserver. And with rising popularity of HTTPS the necessity of piholes webserver answering on port 80 is vanishing.
Furthermore many people are running multiple services on the machine they are using for pihole. The current approach creates problems if you want to run a different webserver like apache or nginx to host a website as you're forced to edit pihole accompanying lighthttpd config.
IMHO this isn't really a reasonable solution. It should be possible to define the webserver port in a simple config file like we're able to change the blocking mode. There is simply no need to insist on using port 80.