5e skeletons are a bit different from skeletons from previous editions (well, I don't know about 4e, but at least before that).
Here's the description of skeletons from the 3.5 SRD:
"Skeletons are the animated bones of the dead, mindless automatons that obey the orders of their evil masters.
A skeleton is seldom garbed in anything more than the rotting remnants of any clothing or armor it was wearing when slain. A skeleton does only what it is ordered to do. It can draw no conclusions of its own and takes no initiative. Because of this limitation, its instructions must always be simple. A skeleton attacks until destroyed."
But here's what 5e has to say:
"This energy motivates a skeleton to move and think in a rudimentary fashion, though only as a pale imitation of the way it behaved in life."
"Although they lack the intellect they possessed in life, skeletons aren't mindless. Rather than break its limbs attempting to batter its way through an iron door, a skeleton tries the handle first."
"When skeletons encounter living creatures, the necromantic energy that drives them compels them to kill unless they are commanded by their masters to refrain from doing so."
These are two very different creatures. One is a robot that does only what it is commanded to. The other is a hateful creature that is, on occasion, temporarily leashed by the foul magic that created it. And if left alone for a length of time, the old-school skeletons will keep doing what they're doing, while 5e skeletons will break free and start being evil.