Not native to the region cause destruction of ecosystem.
Tropical variants change dynamics of the soil. They consume a lot of water and invite Mosquitos like the dengue. Imagine wildlife like Mountain Goats living in the same habitat as Elephants, Monkeys and Snakes and thousands of year old native food being replaced with foreigners. We don't want to end up with the effects on agriculture and its surroundings
India was once part of Australia. They have similar climate, trees and animals. Pakistan is different. It was formed by Indian and Asian plant tectonics hence creating landscapes like mountains. We are more like our western neighbours but unfortunatly, there are some people who are hell bent on Indianizing this country.
Pakistan is predominantly arid. Its climate is similar to that of Afghanistan and Iran. Sadly, the nurseries and governments plant variants like Ashoka, Chandani, Budah, Guava, Neem, Goldmohar, etc which are Indian and Tropical.