The 'One China' policy essentially is about saving face. China is extremely sensitive to not being seen as losing face because of bullying from the West about what they consider to be their sphere of influence.
That in practice Taiwan acts and to all intents and purposes is an independent country doesn't matter as much as being able to claim that Taiwan is a republic of China does.
So, if everybody would just pretend that the 'One China' view is the correct one while Taiwan gets away with being a relatively progressive democratic society everybody wins.
If Trump starts throwing his weight around he might just trigger an invasion of Taiwan and just like Europe and the USA stood by while the Eastern part of Ukraine was annexed I do not expect anybody to lift a finger to stop it.
That's why you don't put unstable bullies in charge of foreign diplomacy with your single largest trading partner and a formidable military power to boot.
Vastly oversimplified but that's about the gist of it as far as I can see, corrections welcome.