Let's make one thing clear, People are extorted all over the world and not only in Pakistan. Extortion is a global issue. Now a fair question would be, how could we lessen extortion?
Well, to answer that, one must understand, why are people extorted in the first place?
It is because the organizations that extortionists belong to, lack funds to facilitate their daily affairs. Now if we strictly talk about political parties and ignore all other entities who engage in extortion, it'd be clear they lack funds for their daily affairs and to top it off Elections are a real pain in the as$.
If ya talk about parties like PPP, they heavy rely on their local MNA/MPAs for both, daily affairs and General Elections. Assistance is, however, provided if the candidate's not rich enough yet ticket-worthy. That assistance fund or Party Fund is comprised of Extortion Money, Institutional Corruption Money, and at times Generous Donations.
Now when ya talk about parties who don't heavily rely on constituency politics are the one ones who need the money most. Although, for the most part, these parties have their vote bank in urban areas, but that doesn't mean they don't need money. Sure, they may need relatively less money, but they will need it. And since they don't engage in constituency politics, their MPA/MNA candidates aren't usually wealthy like that of parties who rely on constituency politics. And that's where the real mess. Now to cover their daily affairs and General Elections expenses, they rely either on Extortion or Institutional Corruption(Provided they are in Government and have a lucrative Ministry). And depending on Political Party, they rely on both Institutional Corruption AND Extortion.
That is the root cause of Extortion. The only solution is Donations from your average joe. Period.
Donations to your choice of political party, especially in General Elections is the only way TO LESSEN extortion.