Why won't European or Canada or Australia defend democracy and provide Taiwan security guarantees and protection?

Because there's a big difference between the situations and you can't really judge a theoretical situation against an ongoing reality. Ukraine is an active war whereas Taiwan is a stalemate of sabre rattling and diplomatic posing. We don't know what each country will do if China invades Taiwan and this is part of what stops it happening.

The security guarantees for Ukraine stem from a 1994 agreement that assured some ex-USSR countries that they could safely give up their nuclear stockpile in return for guarantees that their sovereignty would be protected.

Europe supports Ukraine because it is in Europe, European countries were part of that agreement and European countries do not trust Russia. Not counting Belarus, there's 7 countries with direct borders to Russia, 4 of which used to be part of the USSR, 1 of which is being invaded and the other 3 wonder if they're next.

Whereas Taiwan is not in Europe and doesn't have any historical agreements with European countries.

Canada & Australia have cultural, racial and historical ties to Europe, so it is understandable they often align with Europe.

Because "defending democracy" is propaganda for the common people. It's always economics. The US/Europe will support or even install a dictator if the government is pro-western.

Yep, spreading democracy and freedom is PR. I think there's a historical preference to installing or supporting a dictator rather than a messy democracy. There's several cases where democratic elections delivered a government the US didn't agree with, so they orchestrated regime change.

Exactly. Even in Ukraine, Yanukovych was democratically elected [1] and US was potentially involved in overthrowing him [2]

[1] https://www.oscepa.org/en/news-a-media/press-releases/press-...

[2] https://www.bbc.com/news/world-europe-26079957