Very different circumstances.
Ukraine was (and is) a very small economy literally right up against russia that had long been in Russia's sphere of influence if not under its direct control. Ukraine's fall would have had little meaningful impact on western powers other than losing some face in countering Russian aggression. Specifically to avoid losing that face, western leaders made it very clear from the get go that they would not step in to defend Ukraine, specifically so that they could conserve their strength in case they needed it against China. The universal assumption was that Russia, which was believed to have one of the most capable armies in the world would steamroll the Ukrainians and the country would fall in days if not hours. Only when the Russian advance stalled and it became clear that Ukraine with moderate support could hold out did the west start providing that support, and only after Ukraine made some impressive gains that demonstrated it could not only hold out but potentially drive the russians back did the west start sending serious aid.
Conversely, Taiwan is extremely integrated into the global economy and is a key part of America's pacific power. We have been backing Taiwan for decades. Taiwan is an island, and one with very few appropriate landing sites, making its invasion extremely technically challenging for any power, even one with a strong navy. China, despite its recent shipbuilding spree, still lacks naval and amphibious combat experience, and it does not have anywhere near the fleet size necessary to fully leverage its army's main strengths. We are all freshly aware of lessons learned from Ukraine's invasion: that the strength on paper of countries like Russia and China do not correspond to force projection capability, that providing substantial aid early on is critical, and that modern military equipment is not so powerful as to collapse an otherwise functional country in hours. The amount of aid Taiwan needs is less, and the willingness to give it is greater. Only a major shift in US behavior would cause it to not support Taiwan.