Poodle fur is naturally curly. It can be blown dry straight, just as human hair can be, but will revert to curly. Brushing or combing alone don't really make it either softer or straighter but will keep tangles and matting at bay. This is why brushing alone isn't the way to keep tangles/mats from forming. A brush only smooths thru the outside fur. It doesn't get down thru to the skin.
It is very parallel to caring for naturally curly human hair. After shampooing, conditioner may make the hair/fur feel softer and blow drying will straighten it. Humidity or wetness will allow the natural curl to return. Combing will take out tangles and brushing will smooth. The longer the hair/fur, the easier it is for it to tangle or mat up.
We've all seen the horror photos of dogs who were found severely matted
In less severe matting, it's harder to see from just looking since the tangling/matting doesn't happen from the outside edge in, but closer to the skin/scalp.
This poodle is matted but it's not obvious just by looking. If you try to get a comb thru it tho, you won't be able to. This dog wasn't so badly matted that a full shave down was required.
After a bath, blow dry and getting the mats out
Fully trimmed
If I don't comb thru my boys daily or every other day, the small tangles/mats that develop, like I showed in the other post, will just start spreading and catching other tangle/mats and grow to beyond being combed out but will need to be clipped out. If I neglect long enough, the top photos will be the result.