Hi @Hensun,
I don't work for Instructure or have any official info, so you can take this reply with a bit of skepticism. With that said, The EduAppCenter is really only for LTI 1.1 apps as far as I know, and LTI 1.1 is basically a deprecated standard (in favor of LTI 1.3). if you developed a new app, it probably should have been developed as a LTI 1.3 integration. Since LTI 1.1 is deprecated, my guess is that new apps aren't getting looked at or approved anymore. As a Canvas admin for a higher-ed institution in the USA, I can tell you that we will no longer integrate any new LTI 1.1 tools.
I hope this info helps in some way.
-Chris