having grown up in Delaware County and having spent my summers as a youth on the Chesapeake Bay I believe the answer can be summed up in two sentences:
1) because the Delaware River and it's shoreline in this area is all industrial and ugly
2) The Chesapeake Bay is only a 45 minute drive from there and is beautiful.
Why eat hamburger when you have have filet mignon?
ps: there's not a single decent marina until you get to the C&D Canal.
My step son has worked as a dock hand at the Chesapeake Inn for the last three summers while he was in school and folks coming from the Delaware to the C&D Canal think they've landed in an Oasis compared to the Delaware.
I don't think any of the Delaware River sailors have seriously disputed this. We all agree that about the only compelling reason to sail the Delaware River is the convenience of its location relative to where we live. And that lack of attractiveness is exactly why a high end marina would not be financially viable on the Delaware.
However, I do have a couple of factual disputes.
......the Delaware River and it's shoreline in this area is all industrial and ugly...
There is no denying that there is a substantial amount of industry along the Delaware. To suggest that it is "all ugly" strikes me as a "glass half empty" attitude. There are some interesting things going on along the river, and guests on my boat have often found them fascinating to see. You might not see many ospreys landing, but you might see a V-22 Osprey (and other amphibious aircraft) landing.
There are a couple of interesting towns and other scenery along the river, and Ulladh has posted pictures of them in the past.
......The Chesapeake Bay is only a 45 minute drive from there...
From where I live in the middle of Delaware County, it's 1 hour (much more in traffic) to Northeast River Yacht Club. That's about the closest tributary of the bay, and it's not really "bay sailing." There's a very limited sailable range, and a long, narrow motor down to Turkey Point. So you go looking for better sailing, and much like with sailboats, you get "15 minute-itis." As you cross off the various North Cheaspeake locations because of skinny water and/or too long a motor to get to open water, you pretty much end up at Still Pond, Worton Creek, or Rock Hall (second to Annapolis as a sailing mecca). Now you're in the middle of some fantastic sailing. But you're 2 hours away! So your 45 minute comment kind of misrepresents the issue of driving distance.
...Why eat hamburger when you have have filet mignon?...
If I had to drive 1-2 hours every time I wanted filet mignon, I'd settle for hamburger at home most of the time.
...ps: there's not a single decent marina until you get to the C&D Canal...
As made repeatedly clear here, this all depends on how you define "decent." Put it this way: When the day comes that my lifestyle allows me sufficient time to move my boat down to the bay, I would be perfectly happy if I found a marina there that was comparable to West End, Fox's Grove, or Anchorage. So for me personally, the Delaware River's well known shortcomings have little to do with the quality of the marinas.