Because we (the people who voted for Biden) don't want them. Both were highly contentious issues and the owners and workers for both knew that the next administration would likely kill the project. That's a risk they took.The Keystone XL project plus finish the Mexican wall. Why do a half ass job when both are partially done? We don't need more illegal immigrants and drug smuggling into the US. Also Biden is Catholic so he should be more influenced by the Pope and Pro-Life people than the Pro-Choice people that want everything taxpayer funded. They could probably come up with a compromise of some sort somewhere in the middle. I'm not sure on the Paris Agreement as China and India will continue to be the largest polluters by far and having the US stay oil independent is preferable. The US is going green on its own slowly.
Joe Biden did campaign as pro life and he said over and over that he'd put us back in Paris day one (also the US pollutes more per capita then either one of those countries, they just happen to have populations almost 4 times ours).