Perhaps there were good reasons that President or Governors are given the power to pardon convicted criminals. But it seems like such power has been abused all the time in recent memory.
We know Donald Trump has been abusing his power to pardon for the criminals that should have stayed in jail. And that's absolutely disgusting.
But we've seen state governors pardon criminals as favor for their friends right before they left the office. Didn't Arnold Schwarzenegger or Jerry Brown pardon certain people from their friends' family as political favor right before they left the office as CA governors?
So why should those guys be given the power to get someone out of jail at their discretion if they do it for friends or their loyalists?