First, I believe you'll find that it's THHN or THWN wire.

Secondly, the conformal layer on the wire itself is electrical insulation. The conduit serves to protect the electrical insulation from physical damage that could compromise it, as does the jacket on non-metallic sheathed cable (NM, UF, etc aka Romex).

If the Romex is run across the top of your rafters, as is often the practice, be careful not to set anything directly on it as that could create a hazardous situation by damaging that jacket and perhaps the electrical insulation or even the wire itself.

Because the code requires that the ground wire be insulated, at least outside the house, which eliminates the use of NM cable. The contractor likely though it be better to run conduit all the way to the panel (or maybe local code required it).

Because of the obvious dangers associated with water and electricity, wiring pools is no place for amateur electricians. If you decide to upgrade your pool's wiring make sure you use a licensed electrician who has experience with this sort of work.

Even better, a competent electrician ;-)

Licensing, in my experience, is no guarantee that work will be done correctly, or to code.

Thanks to everyone for your input. I was just curious about the restrictions, Not much chance of any physical damage here in Florida except a hurricane may remove the entire roof in which case it wouldn't matter much anyway. Not much of a problem with squirrels or raccoons getting in and chewing on wires either.

First off I did have a license contractor here in Florida do the wiring and it was done to code and approved by the building inspector. At one point in time (1970's ish) I was licensed in the wonderful state of NY but am getting too damn old (65+) to be crawling through roof trusses.

Randy thanks for catching my typo, I did mean THHN. Also the Romex is run through the joist and stapled to them where they run parallel to the joist not on top of them.

The contractor took out the old gray PVC conduit and put it some pretty looking blue stuff that look like the hose on my pool Vac but I guess it's code approved here in Florida. He stated that there was no issue with the cable itself since it was rated as TC-ER since it is in conduit from the main panel to sub panel. The only thing that had to be replaced had nothing to do with this install. Whoever put the pool pump, filter and salt generator in originally used an insulated 8 AWG stranded wire instead of solid copper for the ground, a big No-No I guess. That had to be fixed before the inspector signed off and I could turn everything back on. Go figure.

What he used is flex ENT aka smurf tube.