And what would Russia gain from invasion? The territory they control now is settled by people who support Russia, adding more territory would add population that would not support Russia, which means guerrilla war which is something Russians try to avoid since the Second Chechen war. Worse, all added territories would be an economic basket case and the current Donbass territories are already big enough headache.
Because Russia is strategically exposed. It was one thing back when Ukraine was under the will of the Kremlin or even simply neutral, but a Ukraine that is openly allied with NATO? That's a red line that the Russians cannot accept. It would allow NATO fighters and bombers within an hour or so strike of Moscow itself. To say nothing of newly developed hypersonic missiles. There's a reason why this suddenly happened in 2014 after the revolution against a pro-Russian leader by pro-NATO movements.
That doesn't even bring into account the problems that the Russians are having with their demographics. Their military is going to be too small to protect the border they have now. The Russia that could throw endless waves of troops at the enemy is long gone. So Russia's only real option at the moment is to move its army forward and take anchor points that they can defend.
These are regular operations, it's just that media portrays them as extraordinary to create impression of imminent invasion, possibly due to foreign crisis inducing USA conservative to obediently fall in line with their government (albeit not as much as they used to).
It was US intelligence agencies that gave the alert. And while they probably have a vested interest in containing Russia purely out of habit--and so we might be skeptical, there is no reason to believe that they're lying simply so the Democrats can force conservatives to act as they want.
If Putin was that stupid, he would have carried the invasion two months ago, before the Duma elections in order to improve elections results. Their current woes are nowhere as bad to warrant Falkland style idiocy.
Russian elections are probably already rigged, so why would he base a very critical military decision on a single election? It's one thing to be skeptical that Russia will attack, but it's another to invent silly theories as to why it can't or won't.