More to the point, it's hard to believe that any Guest would go to Walt Disney World with no dining reservations at all, and then blame their inability to get seated 
anywhere (?) onsite on Guests who, for 
whatever reason, DID make reservations in advance.  
It should be noted that not EVERY diner at every table every time it turned over was using the Disney Dining Plan.    
 In fairness, you can't count that in a discussion such as this one. MOST Guests do not have access to Concierge Lounges and, therefore, snacks.  On the other hand, picking up on the rest of your post - those Guests don't even necessarily need to go off-site, or eat at Counter Service locations.  It sounds like the OP was looking for a table service restaurant, and I find it really, really hard to believe there was NO seating available at ANY restaurant for the entire ten days.  People might need to be flexible.  For example, Rainforest is a great suggestion.  There are at least a half dozen restaurants in the Dolphin and Swan.  There's Bistro de Paris in Epcot.  Victoria & Albert's.  Bongo's.  Wolfgang Puck Cafe Upstairs.  House of Blues.  ESPN Club.  Big River.  These sit-down restaurants (i.e. what the OP was apparently seeking) either don't accept reservations, or don't participate in the DDP, or both.  Flexibility may be required on the part of the Guest, but again, it's inconceivable that there was NO restaurant that could accommodate the OP at any time of day throughout Disney World for the entire ten days.