Without details we’ll assume that all things are equal with your plants in terms of site, drainage, soil type and pH. Hydrangeas bloom on wood produced in the spring on older stems. If you’ve pruned back your hydrangeas, or if winter weather kills them back, there won’t be any old wood to produce new flowering shoots. The plants will probably be mature enough to bloom for you next spring, providing you don’t prune them back too far. The one that’s flowering may be the same size as the other plants, but it could be one year older and therefore more mature than the other two. Just be a little patient—they’ll all bloom eventually.