Some manufacturers try to create their own system applications, mainly having in mind overall look of their user interfaces in their original phones. However, most manufacturers are aware that at the moment, with the current market competition, creating their own applications for making typical activities such as sending text messages or making calls is pointless, especially when customers always have the option of downloading other applications from the Google Play Store than these installed by default. It seems that Xiaomi thinks in similar way, because it was confirmed that in MIUI in the global version firm won't preinstall its own applications for sending text messages and phone calls.
Xiaomi has officially announced that since the launch of Xiaomi Mi 9T Pro, the global version of MIUI system on every phone will be equipped with Phone and Messages applications that were produced by Google and they will be set up as default applications. Xiaomi didn't publish reasons for this decision, but it is very likely that it results from the large differences between legal regulations around the world in separate countries.