Because at the start of the pandemic, when the virus was just starting to spread outside of China, the prase "the Chinese virus" negatively impacted people in o

Because at the start of the pandemic, when the virus was just starting to spread outside of China, the prase "the Chinese virus" negatively impacted people in other countries who "looked Chinese" (although in practice this was "looked East-Asian"). They were avoided, not allowed in certain places, harrased, "why are you bringing the virus here", etc. Now is a different situation, the whole world is now a part of the pandemic. The phrase "the UK variant" or "the Brazil variant" is much less likely to negatively effect people.