People were typing it in Chinese online at the first place, but there were a lot of mainlanders using VPN to post horrible shits, like supporting Hong Kong'sriot police and threatening protestors on IG and FB, and they even hacked a lot of web pages. (While they don't have any ideas about what people are going through in Hong Kong)
So Hong Kong people started to use Hong Kong language, and because it's different from Chinese Pinyin, so mainlanders can't read.
MOST IMPORTANTLY, we really appreciate everyone abroad for helping us spreading the news and having our back.