I'm sure ancient humans ate fruit from time to time, but there are a few factors to consider:
1. ancient fruit was much different than modern fruit, which has been bred over a millennium to be larger, have fewer seeds, more sugar, etc. Ancient fruit would have been small, sour seedy stuff with lots rind compared to what we think of as fruit today.
2. ancient fruit would not only have been extremely seasonal (just a couple of months a year, and only then if you lived in the tropics) but humans would have had to compete with monkeys and parrots and squirrels and insects and scores of other animals to get the fruit -- and the monkeys and parrots would probably have the advantage...
3. the caloric return on eating fruit is not that great -- the alternative back in the ancient days was to kill one of the mega fauna (all of which humans drove to extinction because they hunted so much). One wooly mammoth contains enough calories to feed a large tribe for the better part of a year. In fact, anthropologists have noted that the remains of Home Erectus are universally found in conjunction with mammoth bones -- they apparently lived on nothing but mammoth for a million years.
4. ancient humans lived through ice ages -- they survived through a period roughly 30,000 to 20,000 years ago (Last Glacial Maximum) in which glaciers were a mile deep over what is currently Manhattan. All of Canada was covered in ice -- and yet the Inuit lived there for thousands of years through that ice age -- hundreds of generations. Obviously these people weren't eating any fruit while living on a glacier. Even today there are people groups who live in the far north, such as the Sami, who are almost exclusively carnivorous. In fact there are several know human populations that have been almost entirely carnivorous, such as the Maasai, who live off meat, blood, and milk, and the Comanche, who lived off nothing but Bison.
5. Fruit is almost entirely fiber and carbs, both of which can be entirely removed from the human diet without any negative consequence. I expect that ancient humans were absolute masters of their environments and understood the plant life around them extraordinarily well, but I expect that they lived by the dictum that "animals are food and plants are medicine". They would likely consume plants not for nourishment, but for some other effect.