because that is when the Devon Horse Show is held!!!
It is in Devon,Pa. next to King of Prussia...
2 weeks long...to benefit the local childrens' hospital...the local ladies spend Weeks before baking the Devon Fudge!!
It is to Die For!!!
The Wannamaker Oval is the main ring...used to be the Dixon oval when Mr.Dixon (Philly 76ers owner) sponsered the show
It is also right next to Valley Forge where there is another great Grand Prix usually in April