The reasons bigleaf hydrangeas fail to bloom are generally related to pruning improperly and/or winter cold damage or late frosts. In my climate, they require no winter protection, but comments from many gardeners in other, somewhat milder zones often have issues with winter cold damage - or most likley, late winter/early spring freezes - unless they do protect.

If last year's stems fail to leaf out and all growth in Spring comes from new stems, this hydrangea may require winter protection to bloom reliably. It probably develops invisible flower buds in late Summer or early Fall at the ends of the stems. These buds should then open in Spring but, if it gets too cold and the stems get killed, you get no blooms. Winter protection in the Fall would help with that. I put chicken wire around some of my hydrangeas and fill the inside with mulch. A few weeks after my average date of last frost, I remove the winter protection and use the mulch elsewhere.

If you are pruning it at some point, consider that the invisible flower buds develop in late Summer or early Fall but they then open in the Spring. Thus it is best to prune no later than the end of June so no flower buds are pruned off.

If you have any old stems in Spring that do not leaf out by the end of May, prune these all the way down by the end of May.

You need to be aware that the bloom times for bigleaf hydrangeas will vary widely by location. Mine only begin to start to blooming in late June but will continue until frost. There is no safe time to prune after flowering to ensure next season's flowers. Take any pruning instructions - other than the removal of dead wood - with a large grain of salt. In fact, it is often suggested to avoid pruning completely!!

btw, it is completely possible for last season's growth to leaf out fully yet still not produce flowers. The latent flower buds are far more sensitive to cold temps than are the leaf buds so they can be damaged while the leaves/stems are not.