Here is a photo of a railroad crossing near a road intersection.
The road signals are mounted to slender poles (or even suspended from a cable). Maintenance workers can access the road signals with a truck-mounted boom lift. In contrast, the poles that support the rail crossing signals are built much sturdier and also support a ladder and catwalk. (Ladders and catwalks seem to be common on railway operating signals, too.)
Since there are many more signals than workers, it seems like the total cost to outfit the workers with boom lifts would be cheaper than making every signal easily accessible.
I realize that road and rail signals developed independently, but their common engineering criteria (to hold a light up in the air) should have resulted in road and rail converging on a single lowest-cost solution.