Because that small nation still has a very large military force (though much of it a bit out of date still dangerous),
One of the 'problems' is that Putin/Russia has been spending a lot of money (in relative terms) modernising and training it's forces. See-
And this bit-
For example, the United States Armed Forces has a tooth-to-tail ratio of 17%, meaning that for every combat unit there are around five support units.
Which is a problem for the US military. And other NATO members, eg Germany decided investing in creche facilities was more important than having working tanks. Or modernising it's tanks. The UK is, but although it'll be fitted with a new, improved German gun.
and a rather large finger in the pie in European continental politics by way of the backdoor through it containing large amounts of oil and natural gas?
Yes, well, the black gold has always been a problem. Like Ukraine getting a tad worried that Russian oil & gas will bypass Ukraine, and thus it'll lose the transit revenues it skims off. Or just taking gas and not paying for it. Not sure if those disputes have been resolved yet. But the big man can always ask Hunter, given he worked (allegedly) for one of Ukraine's largest energy companies.
But then Ukraine's in a rather tough spot. It lost Crimea and the break-away regions, and it's got a bit of a problem with neo-Nazis. So that doesn't exactly endear them to the EU. That makes Ukraine's accession about as likely as Turkey, despite it's 'color' revolution to pivot away from it's previous main trading partner to the EU. Who naturally imposed tariffs and quotas on Ukrainian produce.
And then of course the US had a bit of an energy revolution with shale gas. And produces more than it can use, so built a bunch of LNG export terminals.. And then of course would rather prefer the EU got American gas. Even if that's more expensive than simply piping it from Russia.
But such is politics. Russia is a rather huge country that is very rich in natural resources. It's gone from being a large importer of grains to a large exporter. Which also means it competes with other countries agricultural sector.. Which could end up being rather ironic, if the US is heading towards dust bowl conditions and would need to import. And of course there's California. Large producer of fruit & nuts, but running out of water. It was a great idea to grow water heavy crops like soft fruit & almonds in a state that's got a lot of desert, and not much water. It could fix some of those problems with a few nukes* and some desalination plants to water it's population.
But Russia exports fun stuff like titanium, which is a rather handy metal. Ok, so there's a bunch of sanctions preventing US companies from trading with Russia. But the US has worked around that, like during the Cold War when it need titanium for some of it's strategic projects Russia can always sell strategic minerals to China or India instead.
And of course if Biden decides he's going to live up to his Time magazine cover image, he might get tougher on both Russia and China.. Who of course might retaliate, and the supply of minerals and rare earths dries up. That would be awkward..
*power stations, not glassing some of it's problem areas.