Weigelas normally produce their biggest flush of bloom in early spring. The early spring bloom buds form the previous summer. If the shrubs suffer winter dieback or are pruned back later than early summer, they won't bloom the following spring. They can produce some secondary bloom later in the season, but this second flush of bloom is not as prolific as the first.
Because your shrubs are growing in full sun, lack of sunlight shouldn't be a problem.