That happens a lot of the time. But there’s more to it:
The uppermost point of the 5-pointed star is Spirit.
The other 4 points are the Four Elements of Nature.
So when you invert it, you are “reversing the natural order of things” i.e. putting matter over spirit.
Adding to what Temujin said, and taken from my answer here:
The first known writings about the reversed pentagram come from Éliphas Lévi Zahed’s Dogme et Rituel de la Haute Magi written in 1856. In it, he wrote, “A reversed pentagram, with two points projecting upwards, is a symbol of evil and attracts sinister forces because it overturns the proper order of things and demonstrates the triumph of matter over spirit. It is the goat of lust attacking the heavens with its horns, a sign execrated by initiates.”
It’s true that Satanists adopted it and this description became very popular. However, I prefer this other interpretation by Llewellyn:
Does a symbol become evil simply because some group uses it? The association of a symbol with an evil group, leading to the assumption that the symbol is inherently evil is nothing new.
The truth is that a graphic symbol, such as a pentagram, is nothing more than lines. It’s what we put into it that matters. If you adopt it to represent evil, then for you—and for those who agree with you—it’s evil. If you think it’s positive and put positive values into a symbol, then it’s positive.
The Congressional Medal of Honor features an inverted pentagram:
This is America’s highest and most-prestigious personal military decoration that may be awarded to recognize U.S. military service members who have distinguished themselves by acts of valor.
In summary, any symbol can have many meanings and the inverted pentagram is not inherently negative.