Most common reason here in the Northwest is unfavorable weather during bloom.

I have a Blenheim Apricot (supposedly needs 400-500 chill hours and we get less than 120 here). It's also only been in the ground less than 3 years. (it's on standard rootstock too) But it has two things going for it—full sun and I made sure it was well watered. We got a nice crop of 11 apricots this year. Well actually, the full sun may have even been detrimental, since in this climate the warm temperatures during the Winter days subtract from chill accumulation, and the stone fruit needs all the chill it can get here. So I'd have to chalk it all up to the water. I turn the hose on extremely low (almost dripping) and give the water plenty of time to gradually into the soil (maybe 20 minutes to an hour). The water is able to soak deep down this way. 2 times a week during the summer (the summers here are very hot and dry). A lot depends on your climate. You need to make sure your trees are getting what they need, and compensate for the particular climatic factors where you live.

Both cocona and its relative naranjilla or lulo tend to bloom and fruit in the fall or at least after late June. Being from closer to the equator they freak out over long summer days and wait until it gets around 12 hours of sunlight and 12 hours of darkness to get busy. I grow some of them in pots and drag them into my greenhouse for the winter and those plants will bloom and fruit now but the fruit tends to be smaller this time of year. When I visited Colombia they grew Goldenberries (Uchuva) as a hangover cure. I love the flavor and have grown them and most of their relatives here in my garden. Eventually I ended up with some sort of pest that burrowed into the berries making them un-edible so I quit growing them. They say that even the relative 'Chinese Lantern' has nice flavor but I haven't tried it. To me, cocona cooked with a little sugar and a splash of lemon makes a mango flavored syrup or jelly. They are pretty in the garden and easy to take care of, something everyone should be growing.

Those are leaf buds - pears bloom before the leaves expand. And if the trees are young and small you won't get a lot of fruit off of them anyway. In fact it would probably be a good idea to snip off any fruits you see starting to form until the trees have sized up well. Instead of having energy that would otherwise go into development of the top go into early in life fruit production.