The message
from "H Ryder" contains these words:

I am looking for some hardy tulip bulbs. Can anyone recommend some
from personal experience?

until recently I never realised that tulips were supposed to be un-hardy. In
my last garden (heavy, sodden clay in Cheshire) I just planted a load of
cheap "garden tulips" from B&Q (tall things in red and yellow). I never
bothered about getting them too deep (was heavily pregnant when I planted
them so struggled to bend) but did put a bit of sharp sand at the bottom of
each hole. Five years on I'd say that half of them were still coming up and
flowering each year.

You were lucky. Some hybrids are much more longlasting then others.

Hardy, or unhardy, usually refers to cold resistance.

It's not that they are un-hardy, but the hybrid varieties tend to
gradually fade away over years as you've noticed ( its just a matter of
how long it takes). AIUI they do it because the original bulb naturally
reproduces by forming small bulblets after flowering, most of which
don't get enough baking (in the UK) to ever reach flowering size. If
you dig them up after the leaves fade and let them get baked by sun
then replant, they do better, but most people don't bother.

The species are better at reproducing flowering-size bulbs without being
lifted, and also at self seeding .
Janet