I love lilacs!
We just transplanted 2 from a shaded area to an area that gets more sun with better soil. DH read that when transplanting (and I imagine this means also from a pot), it can take several years for them to bloom!
Fortunately, ours popped out a few blossoms, but not many. Hopefully, next year, the shrubs will be fuller and they'll produce more.
Give 'em time.