Because it's in Europe, Putin is mad and last time we let a dictator get his own way it ended in ww2plus they and all the other threatened nations actually really want and need us this time
Balls, we are poking no bear, Russia is threating invasion of the Ukraine and add to that Estonia/Latvia/Poland/Sweden/Finland and Latvia are under Putin's gaze and medling.
No one but Russia (Putin to be specific) is at fault for this mess, no one.
^^ That, unfortunately, is the reality at the moment.
Russia and China's agreement is more about sticking together to prevent retaliation when they do attempt to expand their borders. Planning the expansions at the same time creates a large surface area for the allied to push back on and weakens the standard "over power" strategy that the US typically employs.
However the same principle is true in reverse. If Russia invades and gets bogged down, then china has to support and that starts distracting and draining resources. However china's army is large, the grade of soldiers depends on the units and there are less highly skilled units which china would keep for their own plans on Taiwan. A long war with Russia could hurt China's long term financials as countries, impacted by the lack of Chinese products due to sanctions, would seek their own manufacturing capabilities. China historically see recruitment into warring armies as a natural way to reduce the population growth.. considering they have issues with underpopulation this option is an own goal.
This shapes the length of wars - short and sweet is the order of the day - Putin's bank account is propped up by oil&gas, that is under threat from the push to reduce energy consumption and operate nuclear within the EU etc. The EU could look France to reduce the power demand and that has causes problems to Russian boarder expansion.
The Chinese are in a stronger position but the expansion would have a return on investment - Taiwan and it's semiconductor businesses produce revenue that could pay back for a war. That is why a war for Taiwan would be savage, with a large amount of war Renminbi and Dollars. The US gorilla tactic would be pull the dependency on Taiwan back into the US. China's war would simply result in a cut of semiconductors and sections, the longer the war continues the longer the product goods supply lines for export remain at a risk. So the US only has to keep the production of Taiwan closed towards China. This presents issues for Taiwan and for the world should the Chinese annex the country - naturally a large source of semiconductor fab, the world is then starved of semiconductors and thus competition to Chinese products becomes a lot harder.
The longer the US can keep the Chinese away from war and Taiwan as it is now, the longer the time that countries and companies have to de-risk semiconductor production and limit the threat to their own electronics product exports. If you think Brexit has made exports a pain.. wait till you find you have no semiconductors or the price increases start bankrupting your exporting companies.
The economies are tied, thus sticking you head in the sand and saying don't worry about it has dire effects in the UK's ability to export and manufacture.
Brexit shot the UK manufacturing industry right at the wrong time - Intel et al were looking for fabrication investment outside of Taiwan for this reason. So now the UK has to cope with the cost of import for components that only increases the cost of exported products compared to other countries.
Another own goal for Brexit and short sightedness.