Why does Google in the United States restrict Huawei and not Xiaomi OPPOvivo?

Because Huawei is now exploring the 5G grassroots architecture, Xiaomi, OPPO and vivo are just brands built on the existing architecture. To put it bluntly, it's like these companies are just building blocks on a table. If America doesn't want to play with you, just lift the table. But Huawei set up a new desk in another room, which touched their bottom line interests.