If we listen to pro-Russians themselves, the reasons are clear and obvious -- Russians need a super-wide buffer zone in their "near abroad" against invading hordes of European LGBTQ activists, global warming extremists, transgendered child-mutilators, atheists destroying Russia's new-found religious piety, Protestants, Roman Catholics, Jewish Nazis, globalist-homosexual-financial overlords, the US CIA and maybe even NATO.
Obviously, with all those manifest threats, Vlad the Invader cannot stop with just Ukraine -- no, no, Russia's very national survival requires Vlad to permanently occupy every country once controlled by Vlad's KGB handlers in the Soviet Empire, for starters.
Then Vlad will tell us (or maybe not) if even that's barely enough of a "buffer zone" to make him feel comfy-safe and secure in his Moscow & Leningrad... I mean St. Petersburg, Dachas.
Somehow, I doubt if it will, but maybe that's just me.
</sarcasm>
One of Vlad's many luxury Dachas which require countries of "buffer zones" to protect:
I do not think you read my post.
The concept of buffer is suspect against the sheer range of modern weaponry. Hundreds of miles won’t be of much use. I don’t know what gurus you read. You don’t need to do that. You can do your own research.
MGM140 190 miles
M142 300 miles
StormShadow 340 miles
and of course the basic cruise missiles
Tomahawk 1200 miles+
There are so many cruise missile variants . . . spend some time on the Wiki. (Russian technology in this matter is superior)
Poland is only about 600 miles across. Cruise missiles launched from Germany, west of Poland, can easily reach Russia, and that considers Belarus in between. Poland would not serve well as buffer even if the entire country were disarmed.
Obviously the Russian Oblast of Kaliningrad has a border with Poland, but that is not the center of Russian society. Though useful to note Hawaii is remote from the US and was not even a state, but an attack on Hawaii induced the US to war.
https://www.rbth.com/lifestyle/330666-official-residences-russia-president-vladimir-putin
Most of these appear to be state facilities, like Camp David or Chequers.