One plant used to have a lot of blooms. One never has and I've had it for years. Might not get enough sun. Can I move it?
Why Don’t My Lilacs Bloom? Can I Move Them if I Have To?
Certified GKH Gardening Expert
The soil is probably lacking phosphorus. This is will affect blooming. This article will explain more: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/phosphorus-plant-growth.htm
This article will also help you:
If the plants are not getting enough sun, then yes, this could be attributing to the lack of blooms. Should this be the case and you would like to move them to a more suitable location, now would be the time to do so. Otherwise, you'll have to wait until fall. If you can ensure that the majority of the roots and surrounding soil is lifted and replanted in suitable growing conditions, you'll have a greater chance of success. To reduce shock, trimming may help. Here is an article that you may find helpful: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm