[bobthepanda]

The problem is that to get these effects you need large canopies of trees, and to get that to happen the trees have to take the space of something else. For street trees it takes away land from parking or traffic lanes; for properties it occupies both horizontal and vertical square footage since the sky above the tree needs to be clear. These are unpopular with some political affiliations and interest groups.

[Ar-Curunir]

Replacing inefficient street parking and wide roads with trees is a straightforward win.

[pixelfarmer]

It is like Sim City 1 where crossroads generated traffic, so you'd replace them with parks.