... and when you can simply pour Perovskites into your glass slurry, and turn it into a 60% efficient solar capturing mechanism, and you already have a town square and a road wired up, and all you need to do is replace the panels with a new type, and see how they work... Innovation happens. Some people are just better positioned to take advantage of these innovations when they come along.
And it's not just the positioning of the panels. Designing solar panels to withstand the abuse of a roadway means they're going to be way more expensive to produce. So even if roadways were somehow as good of a place for solar panels, it's still far less economical. The only way this makes sense is if you have nowhere else to put the panels, but in the areas where the has been tried (USA and Australia), there is an abundance of space for solar installations.