Those three dropped for very specific reasons.
Perry was only in first place before he even entered the race. He begin to sink as soon as he started talking and joined the debates. Sort of like Fred in 2008.
Gingrich had one great moment in the SC debate, then was wiped out in Florida by negative ads from Romney.
Cain was only first after two or three others had faded due to poor performances. Then the scandals broke and he chose to not fight them.
Trump has been talking for weeks, maybe a little too much, but he keeps gaining in the polls. His situation is not in anyway comparable to the three you mentioned.
Wishful thinking on your part.
Yes of course there were reasons why each crashed and burned.
With Perry-—awful debate performances.
With Gingrich-—too much baggage and too many ex wives.
With Caine-—too many bimbo eruptions and fast handiwork.
With Trump-—if history is any guide, his big mouth will sink him.