Why are there no subways planned in Xining, Yinchuan, Lhasa and Haikou?

Generally, the reason for building a subway is that the ground traffic pressure is high and the land is expensive, so it is necessary to build a subway to alleviate the traffic pressure.

Xining, Yinchuan, Lhasa and other places do not build subways because they are not needed. The city is too small, the ground traffic pressure is not big enough, and there are not enough people and cars. Building a subway is a bit wasteful.

There can't be a subway in Haikou. After all, Haikou is not big enough. Although the traffic is easy to be blocked recently, there is groundwater underground in Haikou. How to build a subway?

Of course, I still hope that all these cities can build subways! After all, the subway is convenient!