Agree with Cinda's observation regarding rodents eatting tulip bulbs.
I think that may be the major cause of tulips not returning or "disappearing".
They are delicious to most all critters, whereas Daffodils, on the other hand, are distasteful to them, so they survive and multiply.
Last year lost 250 newly planted tulips in a bed and later found the bed had voles.
Put in a vole control system and was able to grow everything there with no losses all summer.
Will try a few tulips there this year and see how they do.
