Shipping water is VERY expensive. It weighs a ton (Well, 270 gallons weighs about a ton....)
RO water is relatively easy to find near most people, and brewing salts are cheap and easy to buy as well.
It would certainly be possible to create a chart of water additions for certain styles, or for emulating recipes the pros use, or other homebrewers use, for their beers. Then it is simply up to the brewer to select what looks good to them and to add the salts to their recipe.
Except people calculate their additions based on mash and sparge volume, and that changes with each person's equipment setup and personal preferences.
So while it's easy to make a statement like; "I prefer to have 180ppm of sulfate in my IPA's.", it's less easy to supply water that gives 180 ppm of sulfate to a beer, while targeting a good pH, on EVERYBODY'S system.
Now, it would be easy to do if they specified that the supplied water, or recipe for water additions was specifically for "Pale Ale, BIAB, 8 gallon Full Volume Mash, 60 minute boil".
You can see that in any case, it would hard to supply a recipe for everyone's needs. Much easier for people to learn about water calculations and tailor their water to their individual needs.
That said, a chart listing ppm's for various beer styles, recommended by various pro brewers or homebrewers, might be useful to someone wanting to see how others do it. But there is still a little variability due to differences in grain bills.
