It's the same mindset that lead to using dispersants on the oil spilled by deep horizon. It's not about science, it's about dealing with a problem that has no easy good solution, so instead of a good solution, just something is done.

Oil companies probably thought that people would be more resistant to buying oil if it needed special effort to dispose of properly. Maybe they didn't even have a good way of dealing with it at that time and just hadn't dumped enough of it yet to realize that it would eventually run down into the water table. Though going by how they handled realizing that burning oil at all was going to have a huge effect on climate, they likely wouldn't have cared even if they did know.

Just like deep horizon wasn't an environmental problem for BP but a PR one, thus they selected solutions that looked like they were trying, that they shouldn't be liquidated to fund a real cleanup effort, and that new deep water oil wells were still worth the risk. Think of all the retirees that they are holding hostage because they put money towards funds that bought BP stock and derivatives!