The West let it happen. They didn’t arm Ukraine quickly enough, nor did they do much of anything to help Ukraine in the decade before.
A decade before the country was run by Russian puppet Viktor Yanukovych. Any western economic or military assistance would have helped Russia continue to own Ukraine politically.
Instead they became closer pals with Russia after the annexation and even more dependent.
The hope was, and there was a lot of evidence it was working, that engaging Russia economically would act as a force against Russian aggression because no one could imagine Russia throwing away their access and economic prosperity by openly invading another country. Also, Ukraine, immediately following the exit of Yanukovych in 2014 had a lot of corruption in government with lots of Russian backed political appointees still there.
At the time it didn’t look like a country that could or would defend itself from Russia even if they were invaded. The taking of Crimea with almost no push-back from Ukraine, and Ukrainian military officers marking their weapons of war to Russia in exchange for Russian military command reinforced this idea.
Had they nipped this in the bud more than a decade ago, Russia wouldn’t have had the means nor the will to invade Ukraine.
Who is “they” and “nipping” it sounds like you’re suggesting would be to flood the (at the time) half corrupt country half Russian owned country with Western weapons to untrained people. 2014 was also when the USA was fighting two wars in Iraq and Afghanistan. Trying in Afghanistan to build a domestic army to defend their government against the Taliban.
You’re looking at Ukraine as the Zelenskyy-era version which has this hope and promise of being a less corrupt place and fighting Russia. Zelenskyy didn’t even take office until 2019. Even then it took a couple of years to learn that he was going to be different than the previous leaders.
I say all of this, and I hugely support Ukraine today! I want more support for them from my government and others, but that doesn’t change what Ukraine was 10 or more years ago.