Presumably because you cut the foliage off when you cut the grass - the foliage should be left uncut for a minimum of 6 weeks AFTER the flowers have faded, and during this time is when they should be fed as well. That's why you see grass verges about with a patch of overgrown grass in late April and early May - it'll be where the daffs were and it's been left by the Council until the 6 weeks is up.

thanks for the response, will the daffs come next year if i leave the foliage to fade this year or have i lost them for good now.

You'd need to feed them, but as they're in grass, you'll have to use a feed that's also suitable for grass. Don't use feed/weed/mosskiller mixes on the grass until the six weeks is up - think I'd be inclined to feed the area that has bulbs beneath with Miracle Gro general purpose weekly, and let the grass get very long and lush in that area, and then cut when the bulb foliage is dying back after 6/8 weeks. Trouble is, that'll be the greenest, lushest part of your grass!

If you have ferns that have gone brown put them over the bulb patch..I had 2 lots in grass. Carlton thrives in full sun & there is a bit of shade. One lot eventually dissappeared as it was under a fast growing bush & it was too dark & dry there. 4 inches down.....is best