Well because the roads are what they are, and "reengineering" them to be something else would take years, would be disruptive, and cost millions. So at best you'll get change when the road needs to be rebuilt anyway, because it's worn out.
You can make a new protected bike lane by just throwing a bunch of jersey barriers on the side of a road. It costs (in relative transportation cost terms) almost nothing.
These sort of things would instantly make the roads dramatically safer.
The only reason this isn't done isn't due to cost, but due to political opposition to having any amount of road space removed from exclusive car use.
Roads are re-done constantly. I'm certain you passed a construction site in the last week of driving around - and I am certain without knowing your situation or where you live.
Cities and communities have massive budgets to just maintain infrastructure.
Each such moment is one where small incremental improvements can be implemented. When a road from 2009 is re-done in 2024, govts can easily enforce that it must adhere to the 2020 guidelines.
Each time a line is re-painted, it can be re-painted to increase safety. Each time a curb or bollard is fixed, it can be fixed to protect pedestrians just a bit better. etc.
Yes, it takes ages. But infrastructure is never finished it's a constant evolution of small steps. It's trivial and cheap (as in: free) to make those steps in the direction of more safety. All that is needed is a will do to so...
