It's important to note the reason the President has the power to pardon anyone for any reason is it's one of the checks and balances, the Constitution is full of them. It's meant as a check to blunt overzealous prosecutions. Note that the President does not have the corresponding power to convict anyone. An interesting set of pardons was when Andrew Johnson pardoned all the rebels in the Confederacy, including Jeffer…
Sorry to break it to you, but as with many things in the US constitution, the reason the President can pardon people is because it's a modified copy of the British constitutional system of the time. The House is Parliament, the Senate is the House of Lords, and the president can pardon people because King George III could and the office of the presidency is a limited term elected kingship. Executive orders are Royal…
Any time you create a second system, you can see similarities to the first system. That doesn't make it a "modified copy"; it makes it a "rewrite that has some similarities".