The problem is bigger than that.

The government has had lobbying for years from the private sector, and the O/G sector has had big money to throw around. They get pushback from these companies when they try to up the 'just in case' fund that is there to cover costs of rehab in case the company goes under. But since that isn't enough, they're often left unmanaged. In the article above they talk about the two easiest examples - mine rehabilitation and orphan well cleanup.

If a company ignores well decommissioning, they can cut costs, suck up as much oil as possible, then declare bankruptcy and walk away from the requirements to clean up, leaving the public to pay for it.

Why should they be responsible for cleanup?

This one is easy. You make the mess, you clean it up. Basic kindergarten levels of societal responsibility.

There’s no law or contract that compels this.

There is, actually, but they're avoiding it by a number of legal loopholes (as mentioned above). Socially/morally, they have the responsibility to do so, but they've managed to legally avoid it/ignore it. Hence the 'shirk'

The argument is that there should be a greater amount of laws and regulations surrounding the O/G or resource extraction sector and their impacts, but often you hear complaints from those employed in those sectors about government overreach and unnecessary bureaucracy/red tape hampering and smothering the free market.

This article is important as it highlights why we need more regulation and the danger of letting these companies continue to act they way they have for years.