US, UK and France have nukes. Under NATO obligations, if Russia strikes the US and manages to wipe it out, UK and France will launch a counter strike and wipe out Russia. Russia has to basically wipe out Europe and the US to avoid a counter strike. But that also assumes a strike on the US that is able to knock out not just every level of command and control, but also take out the US nuclear triad (land, sea and air), which is based all around the world. And Russia is actually mostly a poor and rural country. Russia's wealth is all concentrated in Moscow and St. Petersburg. Remember that Russia's economy has a GDP that is on par with S. Korea and Italy (and has probably dropped significantly since the outset of the war). So, any counterstrike against Russia will only have to take out St. Petersburg and Moscow to basically end Russia. The remaining smaller cities and provinces will all break apart as they all try to grab oil and gas resources that were previously held for the benefit of all Russians. Russia is very aware of this and only makes nuclear threats for the purpose of trying to spook adversaries into not crossing certain red lines.