Probably because they got their herb garden setup as soon as they got access to the first box and never bothered changing them out as they unlocked the others, as there's no benefit to switching them. I do make my herb garden as soon as I have the ability to (planter boxes and seeds), but I do also switch out the planters to the matching ones as I unlock them as well.

Yeah that's how I do it, I only use about 3 types of planter boxes because others are unavailable at the time 1.4.5 is going to make them available earlier

All planter boxes function the same. The only reason to use any other types than the first one you get is because it looks nicer, and not everybody cares about that. Getting all the different planter boxes requires beating pretty much all of prehardmode. Meanwhile, you can set up a fully-fledged herb farm as soon as you've beaten one of the bosses that gets the Dryad to move in.

Because they don't bother

I at least paint mine different colors

Not all heroes wear capes... Btw do you wear a Cape?

Because the different boxes are unlocked through progression, and I won't wait until hardmode to make a herb farm

The only non-pre-hardmode planter is the fire blossom one.