Cymbidium growing shallow roots

[Canadienne]

Hi, I’m new to this forum, I have had orchids for years, but just lately my collection has been greatly expanded to include a variety of easy to grow orchids, like phals, oncids, tolumnia, paphs etc, and 1 great old NOID cymbidium.
My question is this: the cymbidium is 15 years old, is a mini, has grown 5 new bulbs so far, but the roots are very shallow in the pot. I had to transplant it and it’s in bark and pumice, great drainage, lots of holes in the pot. Plant looks great, but why wont it send roots down?