Water bottles, if not cleaned properly with a soap and brush on the inside, will be coated with a bacterial "lawn". Copper prevents that. Lots of bacteria need such a lawn to propagate, only some can multiply without a substrate. So even if the "free" water part won't be desinfected, copper has an overall positive effect on the bacterial content of your drinking water.

As someone who washes my (steel) water bottle at most 1x a week, and drinks ~10-14L of water a week, I've never gotten sick from drinking out of my bottle before.

You can usually tell if the water in your bottle is going bad / filled w bacteria..

Same, except I wash it like once in a blue moon lol.

I have to at least rub the area where I drink otherwise it will smell within less 2 days

I don't usually touch the bottle with my mouth, so I guess that allows for a bit more leeway.

Do you hesitate to drink water from a normal glass or cup as well?

No. I was just explaining why copper is better in that regard, not that I would personally care that much. I do prefer stainless steel, because it is more robust, dishwasher-safe and cheaper.

normal glass goes into dishwasher after every use. Those water bottles are more of a hassle to clean properly