There's 2 main reasons why DNB is the way it is in the States. There's a 100 little reasons, but two main ones...
1) US Visa's are ridiculously expensive. As an artist you need to drop about $2,000 for an American visa. So unless you're booked to play lots of big festivals in a year or a big name who can play over there a lot and ask for a high fee (Andy C, Ed Rush & Optical, Noisia, etc.), it's almost impossible for a younger/less well known producer/DJ to make the numbers work unless you're prepared to travel for weeks and weeks on end playing lots of small nights and sleeping on random peoples couches.
2) US has 30% withholding tax and American promoters often don't pay for flights or hotels and offer "all in" inclusive deals (pretty much anywhere else in Europe you'd have your Fee then your hotel/flight sorted on top of that).
If you get booked for say a festival for $6000 you think, ok great $6,000 seems like a pretty good amount, right? Well say there are 2 members of the group, so that's $3,000 each. Now your booking agent gets their 15%, that's $900. US Federal withholding tax of 30%, that's $1,800. So right off the bat, you can basically take whatever your initial fee is and almost chop it in half by 45% before you've even factored in anything else.
So $6,000 fee - $1,800 (withholding tax) -$ 900 (agent commission) = $3,300. If there's 2 members, that's $1650 each. Now both artists have to sort their own flights. Let’s say an average flight from UK to US is about $1,000 (can vary a lot of course). Now we're down to $650 each. Maybe if you're lucky you had a hotel sorted for you... you probably didn't though. So let’s say another $150 for a hotel. Down to $500 each. Now there's always going to be some miscellaneous spending (food, drinks, trains, cabs, etc.) but let’s just be really conservative and say you only dropped $50 each (not bloody likely lol). Down to $450. Did I mention that's American dollars? Your $450 is worth £278 back home in the UK. Yes, believe it or not, your epic $6,000 festival has now whittled down to a whopping 278 quid.
Obviously with the above example it doesn't make much sense to do one-off shows and fly home, so you really need a full weekend of shows minimum to make it even worth it. And with withholding tax there are some provisions/treaties to avoid double taxation from the UK/US, but basically when you get your statement from your agent the next month, that's what you're seeing.
This is why we can't have nice things.