Let's add some facts to your claim, instead of all that thurr hyperbole...
The Canadian National Energy Board approved the pipeline in March 2010 but Mr Trump's predecessor, Barack Obama, did not issue the presidential permit required in the US.
Then, around July 2020 -
The U.S. Supreme Court refused to let construction start on TC Energy Corp.’s Keystone XL oil-sands pipeline, rejecting a bid by President Trump’s administration to jump-start the long-delayed project.
The justices, without explanation or noted dissent, left in force part of a federal court order that blocks use of a key federal permit. Although the justices cleared the way for other oil-and-gas pipeline construction projects to use the permit, they refused to do so for Keystone XL.
The rebuff means almost all Keystone XL construction is delayed until 2021, according to court papers filed by TC Energy. The company told the high court that lifting the order probably would have let construction start by August on the pipeline, which would carry more crude than some OPEC members produce.
So the reason that the K-XL wasn't built under Trump boils down to legal blocking by judges that favored Obama.