Why does only one of my three lilac trees bloom?

We have three lilac trees in our backyard that have been there for over 30 years. We trimmed two of them down to only a few feet on the advice that they would grow back fuller. 20 years later one is still quite small, the other has grown back to about 7 feet tall but neither one ever flowers. The larger one is on the same side of the yard as my third flowering lilac so I think they both get a decent amount of sun. I have fertilized in the past but to no avail. We live in north New Jersey, USAWhy does only one of my three lilac trees bloom?
Actually fertilizer is the wrong thing for lilacs. They are like dogwoods, if you give them too much nitrogen they won't flower. Pruning is good but it has to be done properly. You need to prune in thirds. That means that you prune away one third of the large older growth then wait a year and prune the second third , etc. Sun is important, they need half a day of sun. So if you have mature trees around that have begun to shade them that could be a problem. Below are some links to help you.Why does only one of my three lilac trees bloom?
You must have shocked the other two.