Cause 1: wrong place
The wisteria likes a spot in the sun or semi-shade. Less than six hours of sunshine a day will not make it happy. So the east, west or south side of the garden or facade is fine. If the Wisteria is in the shade for a large part of the day, no flower buds will be produced.

Cause 2: Poor soil
Wisteria likes soil that is rich in humus. So give it extra nutrients. Also make sure that the wisteria is not too dry. In the open ground it can take a beating (read: wind and weather), but if it is in a pot, then in a harsh winter you have to protect the root ball.