Few reasons
1 resource and man power
Gov agencies cant go against every body at same time one as these people are not small thugs which on going investigations all this takes alot of man power and alot of resources to have major investigation against one crook and keep minor eye on other
2nd public opinion
Pmln and pppp have major support in punjab and sindh and suddenly if all are being charged at same time they will go crying its army whos doing all this
And people will go crying in street which will cause major problem
3rd public image
With proofs and verdict judiciary and agencies show that they are working the country, and these people are actually corrupt so next time they will get benefit of the doubt they are actually doing the job and dont have any agenda