It is a technical issue.
Look at this table for an indication of the number of different protocols out there. Only those rows which are used for HTTP (notably 80, 443, and 8080, but also see 8384) can use a HTTP proxy, because only those rows use HTTP.
Everything else, e.g. FTP, SSH, SMTP, IMAP, POP3, Gopher, SFTP, DHCP, NTP, and many many many more, cannot use a HTTP proxy, because they are NOT HTTP.
If you don’t understand an explanation of why Syncthing cannot talk over HTTP, I’m afraid you just have to accept it. You can’t say “I don’t understand any of this, but I’m sure it can be made to work”.