If they're not just late (they all are, this year) and genuinely don't flower, did you cut the leaves back last year? Cutting the leaves off before six weeks have elapsed between end of flowering and cutting means the bulb can't build up food supplies for the following year, necessary for flowering. Otherwise, they were possibly too dry and couldn't get enough nutrients. Feed them now and for the next 2 months with something - you can either put handfuls of growmore and rake it in (will do for six weeks) or get some Miracle Gro general purpose and water it on weekly.

Planting too shallowly can also cause this...daff bulbs should be planted 3x the depth of the bulb, which normally means 6 to 8 inches deep.