Two answers for this:

1. If a map created for an existing published setting is not intended for sale, posted only here (for example), I don't see a problem. Some people have created maps for published modules that didn't have a given map in the product, so a cartographer here created those missing maps posted here. There didn't seem a problem.

2. World maps for some existing published worlds, like Paizo's Golarian isn't available anywhere online. There are a couple fan created maps, but official maps of Golarian can only be purchased from Paizo. This would seem to mean that one couldn't or shouldn't recreate Golarian and post, as there seems to be some kind of IP issue in doing so. You can't even post a Golarian map to gamewiki - according to the license.

I don't see issues of conflicts with non-official cartographers, or a case of bad taste. Map the world you want to play, even if the world is a published one - why would there be a problem.

That said, I primarily create worlds or regions that have no existing map, nor is officially published - except of course my own published setting. I don't make fan maps, as any map I create has the potential to becoming a product to sell. If due to IP or license prevents me from selling such a map, in my mind, that's a waste of my time. I won't generally create maps that I can't potentially sell (except commissioned maps which I'm being paid for to create, but cannot sell myself.)