She was Austrian, a country that France had been in war with for years. The French did not want a foreigner on the throne, especially not an Austrian.
Also, even before she came to France, the revolution was already smuldering because of the financial disasters of Louis XV which he did to the national treasury. France was already almost bankrupt when Marie ZAntoinette stepped in the picture, and because the French needed someone to blame it all on, and she was Austrian, she was the perfect victim. The people tried to make all of France believe that she had no concern for her people, spending money on wigs and dresses and throwing wild parties while the population was starving and desperate.
The people did believe it, although she was completely innocent and killed her and her husband, destroying the whole French monarchy and the French credibility all around the world for as far as the French had that anyway.