Root collar excavation/ stem-girdling root investigation and treatment.
It's too deep in soil.
Mulch 1-hand width deep with wood chips, with a 1-hand wide gap at the trunk ( once you find the root collar).
Deep root irrigation needle for watering.
Pic of retaining wall. How much soil was added or taken away?
It's multifactorial.
Lots claim to be arborists. Some lay-people think it's the politically-correct name for the tree-cutter-guy.
Last night I heard about an arborist dumping a tree on a power line.
There is no "studying care of trees" when killing trees or removing dead trees... That's a service an arborist may or may not perform.
I do lots of killing of dying trees...sometimes arborist training is the knowledge-base I rely on to indicate to the client their tree is dying or higher risk, and why... But no care and study of trees is involved in removal, which is the basis of many tree service companies work.
I know a two local Certified- Arborists with loaders, big chippers, big chip trucks. These tools are for large tree demolition. I think they are likely going to keep demolishing big trees, as cable-and-brace support systems and soil drenching with fungicides doesn't make the payment on an 18" chipper and big trucks.