Why did the Soviets want satellite states?
They wanted a defence against future attack from the West.
One can analyse Soviet policy towards Eastern Europe in both the short term and the long term.
In the short term, the creation of Soviet satellite states can be seen in the context of the post war world. A series of Conferences by the Allied leaders had pretty much divided up Europe with the Soviets getting the East.
Moreover the Soviets were advancing West and so Stalin was in a position to occupy these countries as the Red Army advanced. It was also the case that some of these countries, for example Romania and Hungary had fascist governments whose armies fought alongside the Germans for example at Stalingrad.
Finally the emerging rivalry between the USA and the Soviet Union emphasised Stalin's fears for the future.
This last point is linked to the Soviet Union's long term fears of the West. Three times in the previous 30 years the Soviets had been attacked, in 1914 as Russia, in 1917 as the west supported the Whites and in 1941. Losses can be measured in tens of millions so this was why in the long term the Soviets saw a need for satellite states.