inotify requires you to hold open fds for all the dirs and files you're watching iirc, so in repos that large, you'll be crushed by the file-descriptor-per-process limit.
It doesn't, you might need to tweak its limits via /proc/sys/fs/inotify/max_* on such repositories, but those limits are not the same as the much lower open FD limits (as in ulimit -n ...).
I've posted some details explaining why gitstatusd doesn't use inotify in https://github.com/romkatv/gitstatus/commit/050aaaa04b652e15.... The short version is that the default max_user_watches limit is much too low to be useful for gitstatusd and I cannot ask or expect users to change their system settings.