Vinyl chloride, when burned, can create poisonous byproducts such as phosgene and carbon monoxide. Vinyl chloride that leaks into the environment is a carcinogen that can cause damage decades into the future. It's a tradeoff, but probably a good one. We can deal with the acute danger of poisonous gas by temporary evacuations and air filters. Once a carcinogen is in the ground or the water, though, it's much more difficult to get it all cleaned up.

It boils at 7.88°F.

It sounds like without pressurization or chilling the risk of an explosive release was deemed higher than the risk of burning it.

Picking up liquid off the ground seems very difficult, I imagine.