Why don't Poland, Hungary, Bulgaria, Romania and other countries join the Soviet Union?

On the one hand, from the perspective of eastern European countries, they are unwilling to give up their sovereignty and become a part of the Soviet Union. Therefore, on the other hand, if the Soviet Union "annexed" these sovereign countries, it would be tantamount to aggression. As a satellite country that has been operating behind the scenes since World War II, there is really no need for the Soviet Union to be accused of "aggression".

On the other hand, from the Soviet point of view, the original Soviet confederacy system was unstable. It's good to join too many countries. Moreover, historically, among the member countries that make up the Soviet Union, except Russia, other small countries are basically "nobody". They were tied into the Soviet Union, which not only exploited a loophole in history, but also became an established fact. However, Poland, Hungary and other countries are quite famous in history ~ ~ Once they were annexed by the Soviet Union, the behavior of the latter was completely different ~ ~ For example, Romania, Bulgaria and other countries were originally part of the Ottoman Empire, and later Turkey joined NATO. Once the former is openly incorporated into the Soviet Union, it will inevitably cause a strong reaction from the latter (even the whole NATO). These are not what the Soviet Union wants to see.

In addition, there is another point: one of the main reasons why the Soviet Union was able to confront the West at that time was to nominally "unite with the Third World". If the Soviet Union forcibly incorporates these neighboring countries into its own part, it will inevitably lead to its international isolation and even push the Third World to the west. This was the biggest concern of the Soviet high-level at that time!