~90% of cases are slander. Canaanite child sacrifice is only talked about in the Yehubor Bible, for example, no outside sources. Greek and Germanic human sacrifices are christian propaganda, and "animal sacrifices" were misinterpreted blessings of the food or rituals to help the slaughtered animal reincarnate.
That being said, some peoples and cultures did do this and that sacrifice. Some were warned, some were left to their own devices because their conscience should've known better.
The Gods also frown upon laziness, and yet many who follow them are lazy, and so on.
If the Gods only "allowed" to happen what "they want" to happen, you wouldn't have the sentience to ask this question.
Ignorant people will do what ignorant people do, and it does not reflect on the Gods who are only good, fountains of good and without blemish.
"Why God allows x", "why God didn't stop y", "doesn't God dislike z" are mentalities of an Abrahamic origin, these weren't even questions in the Hellene world, for example.