Why did abbasids lose control of their empire?

Answer 1
because people rebeled

Answer 2
The reasons for the eventual fall of the Abbassid Caliphate which occurred in 1100-1258 CE are the following.

1) Corruption: The Abbassid Caliphate had become one of the richest and most prosperous states in the world at that time, changing its leadership from honest brokers of power (Amir al-Mu'aminin - Prince of the Believers used to actually mean something) to individuals more concerned with money. This created strong resentment from those who were outside of the Abbassid purview.

2) Mawali Inclusion: The Abbassids were an Arab Caliphate (as opposed to the Samanids who were a Persian Caliphate) and were expected by many Arabs to treat other Arabs better than the Mawali. However, the Abbassids consistently treated Persians equal to or better than their Arab brethren which created animosity and a sense of betrayal. Many Arabs saw the Persians as the major backers of the Caliphate and that they were a tool for Persian interests. It was also perceived that the Persians were first servants to the caliphs but climbed way up the social ladder to a place they did not belong.

3) Turkish Armies:
Armies like the Mamluk (who were retained by the Abbassids for the defense of the Caliphate) were Turks who defended an Arab State. Beginning in this period, they began to realize that they had the capacity to create their own states considering how vast their powers were as a military. This idea also came to the fore for Turks outside of the Caliphate. As a result, there were Mamluk uprisings, Seljuq attacks, and other Turkish Armies turning against Baghdad.

4) Rise of the Mongols:
Hülegü Khan put the final nail in the coffin by massacring Baghdad and a number of Persian cities when he conquered the territory for the Great Khanate.