Answer: Probably the most common reason for forsythia not blooming well is pruning at the wrong time and cutting off all the flower buds as a result. (The best time to prune is immediately after they bloom.)
But in your case it sounds like winter cold might be the cause. Often when you see forsythias with those golden ankles you will then remember a particularly cold winter blast when there was snow covering the lowest part of the plant -- which is also the part blooming now because the snow insulated and protected it from the cold -- the remaining buds having been winter-killed.
Q&A Library Searching Tips