Why do they do this? Because plastic in landfill is apparently the worst thing that can happen to plastic waste. Instead of containing the toxicity to the local area of the landfill, it is spread everywhere via the roads.
Places in India make it a legal requirement.
I feel sorry for India - all those schools and houses with toxic roads running right in front of them.
The biggest argument I have heard against plastic roads is "well roads are bad for the environment anyway, so no reason not to fill them with plastic".
https://www.theguardian.com/sustainable-business/2016/jun/30...
Vested interests hard at work to legitimize plastic roads:
https://www.rmit.edu.au/news/all-news/2023/aug/recycled-plas...
And those pesky environmentalists getting in the way of progress:
https://www.theage.com.au/national/the-science-stacks-up-for...