No, if you do things right, you should have nitrates like that.
Perhaps people overfeed, or overstock, or underskim. Perhaps as rock ages it loses it efficacy unless you can regularly "cook" your rock every few years. Sand gets old.
I can tell you that any tank I've kept my ritteri in has always suffered insanely high nitrate levels and that was the impetus to try a sulfur reactor. I don't know what it is about that anemone because I do not feed it anywhere near as much as I do my other anemones and they do not promote a nitrate buildup in the tanks they are in. In all fairness it may not be the ritteri, it could be coincidence. I don't know what's going on, but I decided I wasn't living with 50-80ppm nitrates any longer.
In my other tank, I feed a little generously, and there are some compounding factors that contribute to a slight nitrate buildup in there as well.
1) I added a copperbanded butterfly in the summer who will not touch any kind of food that's been dried (flakes, pellets or otherwise). So I have to feed frozen foods on a daily basis, or meaty foods like a clam, for his benefit otherwise he starves. But this adds to the bioload of the system.
2) I added a dendrophyllia a few months ago and was shocked at how much food this coral requires.
3) I have gorgonians and I can't help but try to feed them as it's just "way cool" watching them eat.
Nevertheless even with these factors working against me, as long as I keep my skimmer clean, and stick to my monthly water change schedule, I still only get nitrates in the 15-20 range. I'd be happier if they were lower but I'm not worried about it. And I know they would be lower if it wasn't for the basically daily feedings of mysis.
I think though another reason is that a coil denitrator is a cheap and easy thing to try. So a few people have decided to give it a whirl. I think it's an awesome idea for say a FO tank, where people usually pay less attention to the levels. 100ppm NO3 in a FO tank isn't unheard of... so why not throw a $30 piece of equipment on there that helps lower that value.
Anyhow just my $0.02. I'm sure others have their own reasons too.
