Lilac not blooming

Question

My Lilac is about 20 years old, and very large. It gets buds on it and than they dry up. I have 2 flowers that opened this year. We have cleared away any bushes close around it. It gets mostly morning sunshine for about 4-6 hours. We have a lot of oak trees around our yard. Some across the road. It has shade from across the road trees until about 9:00 AM. Than full sun 1-2:00 PM. It has grown to about 8-10 foot tall. We never fertilize lawn or trees. I did bloom when it was smaller for a year or 2.

Answer 1

One possibility is lilac bacterial blight
http://extension.oregonstate.edu/gardening/how-recognize-treat-and-avoid-lilac-bacterial-blight

Here are some other possibilities:
https://ask.extension.org/questions/188959

https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-bush-not-blooming.htm