The Ukrainian situation was being managed quite well as a local conflict.
Historically, the USSR hasn’t engaged in any direct conflict with the west (I think because they knew they were at a huge disadvantage militarily). But the proxy wars in Vietnam, Korea and some other places in Africa and Asia were successful for them because they kept their involvement low level and restricted to supplying funding, arms and “advisers”.
NATO (and formerly the USA) had adopted this same successful strategy in supporting Ukraine against a very depleted Russia and doing well with it. Why change something that’s working so well. Russia will never actually conquer Ukraine. The much stronger USSR had to give up in Afghanistan, and will still have to give up in Ukraine if European countries support Ukraine.
I don’t think western countries will send soldiers to fight Russian soldiers in the foreseeable future simply because there is no need to. The only exception is likely to be when Russia breaks apart in 10-20 years time.
Any foreseeable WWIII would involve China as the adversary, not Russia. China is only likely to fight a WW over the South China Sea and Taiwan, they wouldn’t even get directly involved in a Koran war re-starting. China is strong enough to fight a WW (on its own doorstep) but Russia can’t even successfully fight a single ex-satellite state.