Low level officials can be eliminated through missile strikes.
If if had to guess, Maduro could have been take out with a GBU or two, but the US holds a grudge against him so they took him out to humiliate him, and send a message to others.
There's a big international diplomacy difference between assassinating a leader and forcibly extraditing one on drug charges.
Not too many countries will go to the mat to support a leader who was engaged in narcotics trafficking, if the US is able to present a viable case (which they seem to intend to, if he's being charged in US federal court).
If if had to guess, Maduro could have been take out with a GBU or two, but the US holds a grudge against him so they took him out to humiliate him, and send a message to others.