People just make mistakes, so devs make them too. Their assumption was that Mi9 would soon move into MIUI 10.3 so they stopped releasing patches.
But that was in March 2019 (!) and Mi9 china stable never went into 10.3, chinese still release ROMs with latest security patches (latest is China Stable MIUI V10.2.33.0 – PFACNXM).
Since then half a year passed (!) and numerous people here started to ask what happened and why there is no xiaomi.eu support for Mi9 stable. They were told that they should "blame chinese". When I pointed out that chinese still support Mi9 and asked for renewing xiaomi.eu support for it - all I got was pure hate. Not only from other users who told me to be grateful for a free work. The devs told me "who the hell are you" and kindly advised that I should leave.
That's basically the whole story. When someone gives you something for free you have basically no rights at all. They can take it back from you and you should shut up. And be thankfull, right?