They are also involved in many big money making semi legitimate or more white collar rackets...

The higher ups in a lot of cases have $ and are not as greedy.. Not being as greedy creates more loyalty and combine that with the plea bargain philosophy leads to less rats...

They are very secretive also so even when someone does rat they don't know as much as someone in another family does.

They have also always been very powerful with smart leaders and the big money making rackets getting passed down to the next generation which was taught how to be smart and low key...

And of course they have been lucky in certain cases.... I don't remember the whole or exact story but I bieve when Fish ratted he could have potentially brought down Barney and other higher ups but something occurred that minimized his potential damage...