Many bulbs have retractile roots that allow them to self-adjust their depth.

And also it could be because so much mulch has accumulated and decomposed on top of them over the years.

I find it impossible to dig up daffodils that I planted no more than 5 inches deep 25 years ago, because now they are at least a foot deep in clay soil.

The new bulbs appear at the base of the old one, and tend to expand down a bit, ... and each year the new bulbs are a bit lower.

Plant them at the recommended depth for your climate (3-4 inches) and let them do it again.

This makes sense. The bulbs are smaller than the original ones. The average size is about 1 1/4 to 1 1/2". There are so many of them. I'm not sure if my new beds are large enough for them.

I still need to dig up the Iris and Daylilies.

I'm much too lazy to dig up my old daffodils. Some of them were planted 20 yrs ago, (Ice Follies, Salome, Mount Hood) and since they are still coming up and blooming well, I let them be.