At the risk of sounding pedantic, it most certainly IS an option.
Dozens of NATO countries, including the USA, possess well-equipped armed forces - we have been told repeatedly that many of these countries have shipped high-tech weapons and munitions to Ukraine in advance of this horrific development, so it's safe to presume that this equipment is at least as good as the best already present in the Ukrainian military.
The troops and equipment exist. The will to use them however, is absent. Macron, Johnson, Trudeau and Biden, amongst dozens of other leaders, are very happy to talk about how unacceptable Putin's naked aggression is... But actions speak louder than words, and the actions taken thus far demonstrate to Putin that actually, provided he essentially pays a cash penalty, his annexation of Ukraine is acceptable to "the West", because the major players in NATO don't feel the urge to go any further than that.