US evicted the Taliban from Kabul in two months. Russia has taken 20% of Ukraine after six months. Lets be honest, nobody thought the Russians would be invading for six months.
The Taliban, having a total force under six digits in 2001, had approximately 15,000 casualties during the initial invasion, compared to 12 US troops who died between October 2001 and March 2002. Of course, given the numerous militias and ragtag nature of the Taliban and its allies from 2001 onward, a reliable headcount is going to be difficult to obtain. However, the United States invaded with assistance from local militias opposed to the Taliban, along with over a dozen other countries and UN backing. (Granted, all of this dazzling success, 20 years on, was for naught, since the Taliban is now back in power with over $7 billion in US military tech to play with that got left behind.)
You're seriously comparing that to a conventional peer-to-peer war between a fraction of Europe's largest army on the home turf of Europe's second or third largest army (depending on how you count force totals)?
Pull the other one.
One key difference must be in Build Strategy.
The US could act in Iraq and Afghanistan with no fear of confrontation by a peer enemy (though of course the US had to deal with plenty of lethal aid in the form of IEDs smuggled in from Iran and Pakistan). There was no chance of suddenly being embroiled in an air war.
The Allies in Ukraine (on the other hand) have to deal with the very real possibility of formal intervention by NATO forces. They can't, can't build a bigger air force than the US. They can't ignore the mass of high-tech tank-killing weapons in the hands of the UDF. And they have to penetrate well-defended modern fortifications that have been laboriously constructed over eight years.
They need to neuter NATO air power and AT weapons by deploying artillery in all its modern forms, backed with Soviet-era levels of ammo-production. All this while deploying only 200K infantry in-theatre (which seems to be a political constraint).
So their core build strategy hinges on massive artillery coupled with drone-jamming and deterrent levels of air defence. Which all makes for slow going.
We might expect to see a modest speed-up after the Kherson elections frees up men for other uses. Or if the UDF tires of its casualties, God help them.