There were a number of reasons the people of Ukraine, the EU, the International Monetary Fund and the USA were against the work of Viktor Shokin and why he was replaced.
Besides the war at the eastern border of Ukraine, the primary problem President Poroshenko faced was eradicating corruption within it's sovereign borders. All one has to do is realize that the previous president, Yanukovych, and his activities were to know the corruption was rampant. The national military was disarmed and the Oligarchies throughout the country were provided weapons and uniforms to form their own militias. The Oligarchs under Yanukovych were the organizers of the economy, so everything went through them. Replacing that organization and rearming of the national military while disarming the militias didn't happen overnight.
While seeking to strengthen the domestic economy and government infrastructure the IMF lead the charge against corruption in Ukraine. When it was obvious that wasn't going to occur, Shokin was viewed as the cause.
13 February 2015
“The nomination of Shokin is a shock” (click here) – shouted the participants of the manifestation in front of the Ukrainian Embassy in Warsaw. Ukrainians, Kazakhs and Warsaw residents gathered in front of the building and protested against the most recent changes in the Prosecutor General’s Office in Ukraine and the nomination of Victor Shokin to head the prosecutor’s office.
Representatives of the Open Dialog Foundation, which organised the protest, were drawing the attention of passers-by and the media present on location, to the attempts by the Prosecutor’s Office to protect and cover for the people responsible for the massacre on Maidan. An appeal was also filed with the Ambassador and addressed to the Ukrainian President, the Prime Minister and MPs, in which Shokin’s nomination was heavily criticised.
From the Irish Times
March 29, 2016
By Daniel McLaughlin
The European Union (click here) has welcomed the dismissal of Ukraine’s scandal-ridden prosecutor general and called for a crackdown on corruption, even as the country’s political crisis deepened over efforts to form a new ruling coalition and appoint a new prime minister.
Ukraine’s parliament voted overwhelmingly to fire Viktor Shokin, ridding the beleaguered prosecutor’s office of a figure who is accused of blocking major cases against allies and influential figures and stymying moves to root out graft.
“This decision creates an opportunity to make a fresh start in the prosecutor general’s office. I hope that the new prosecutor general will ensure that [his] office . . . becomes independent from political influence and pressure and enjoys public trust,” said Jan Tombinski, the EU’s envoy to Ukraine.
“There is still a lack of tangible results of investigations into serious cases . . . as well as investigations of high-level officials within the prosecutor general’s office,” he added....
An investigation into The Bidens doesn't even enter the picture. Shokin was a died in the wool Russian sympathizer. He won't bring charges against those that murdered all those people in the Maidan and he was not seriously pursuing the corruption left behind by Yanukovych. He was hostile to the priorities of President Poroshenko. I think the war on the eastern border was more the focus of the president and it wasn't until the EU, the IMF and the USA started to insist Ukraine deal with corruption did Shokin finally come into view as a problem.
It is sometimes difficult to understand how such corruption could still exist after a revolution that lead to changes in the constitution, but, these people existed under Russia oppression for years under Yanukovych. They were used to coping with the existing corruption and to some extent corruption has its own economy. So, a new democracy was moving forward albeit slowly and with enormous problems, including the pressures from Putin; the political infrastructure was still very fluid and allies were not necessarily easy to identify.
President Poroshenko was a businessman when he took leadership. His focus was moving Ukraine forward to encourage growth and inclusion into a European market. One of the reasons Ukraine wasn't involved in European markets before the revolution was because Russia backed Yanukovych and Yanukovych was corrupt to the core. His palace alone and all it's opulence came as gratitude by Russia.
Poroshenko had to change all that and he never focused on the fact his Prosecutor General was part of the problem. Part of that was political and appearing competent, but, his new allies insisted he move forward before sincere relief and the European markets could be open to Ukraine. That is the reason Shokin was removed from his position. It had nothing to do with Biden, except, the Vice President put an ultimatum to Poroshenko. That was the only involvement VP Biden had in removing Shokin and it had nothing to do with his son. It was about moving Ukraine out of it's vast corrupted Oligarch networks.
I might add at the time all this was going on the war in the east, vanquishing corruption, encouraging economic growth, President Poroshenko was involved with Germany, Russia and the rebels in the east in writing two treaties. First was Minske I that was violated by the eastern rebels and Minske II had the same fate. Putin's promises of ending the war didn't even come close. Instead, Russia armed the eastern rebels.