Same reason they are not in EU, tarrifs.
There will probably be a lot more starting next year since they are building a factory in the EU which is scheduled to start production at the end of this year. That bypasses tariffs.
"BYD has sold 19,241 fully electric and plug-in hybrid vehicles in Europe last month, a 255% soar from the same period a year ago."
Small numbers, but I am pretty sure they're in Europe. https://eletric-vehicles.com/byd/byd-sales-in-europe-more-th...
Edited: Tariffs vary across Europe, particularly in non EU nations.