The reasons why the swing-out cylinder revolver has supplanted the top break are several.
A solid frame will out shoot and out last any top break.
A solid frame is simply stronger size for size, and weight for weight.
The top break's frame is a two piece affair joined by a relatively weak hinge and a necessarily small, weak latch.
The weak link in a top break is the hinge and the latch, and there's only so much that can be done to fix those.
A solid frame has proven to be a more accurate pistol than the top break whose hinge and latch allow the frame and barrel assemblies to shift.
Bottom line is, under head to head competition, the solid frame, swing out cylinder revolver just out performed the top break.
Keep in mind that competition wasn't only against cheap top break guns.
Remember, S&W and Colt competed against Webley, and Webley's weren't cheap junk.
In order to be competitive today, a new top break would need to have something to offer other then being an oddity.
The top break design just doesn't have enough to offer.