This of course applies mostly to areas that are hot for a good portion of the year.
And I have the same concerns as you about the reflective pavement.
That is, constructed shade structures that provides shade without being unpredictable living things.
There are probably real problems with that approach too. What are they?
Note that buildings are also shade structures but they contribute to the heat island effect.
Tree trimming and eventually removal can cost 500-1000+$ for older trees which you eventually need to do to avoid having limbs and eventually trees fall on nearby cars. Roots damage local pavement again if you let the trees grow large enough. They also start taking up significant space requiring much wider sidewalks.
Of course you can remove them and add new trees regularly, but that’s another cost and tends to upset locals. Etc. granted his is usually in comparison to an empty sidewalk as it’s unusual to have other forms of public shade.
A big one regarding more trees is more maintenance, you've already pointed out how terrible maintenance can be, and lawns alone are an incredible example of just how inefficient we handle plants in the name of some arbitrary aesthetic, tons of water wasted, many hours spent trimming things to some ideal size that turns out to be terrible for the plant itself, etc.
Of course my paranoia doesn't ignore cool pavements either; the reflectivity does bring some mild worries: some skyscrapers are known to cause large amounts of concentrated reflective heat, but those are due to the more mirror-like reflective properties of glass rather than the diffusive matte grey/whites of these pavements. I also worry about visibility, could we end up having a "snow blindness" effect? Would driving be affected as the harsh unnatural dark contrast of a typical road is very easy to spot compared to...everything else. I'm ofcourse aware not all roads are this black but you can't deny bright yellows and whites of road markers on a deep black road would be easier to pick up on than on a greyish road.