It had a military advantage. It doesn’t anymore.[0] Taiwan has not been sold modern equipment, while China has increased military spending and operational capability.

Being an island, Taiwan always had to rely on holding off an invading force for as long as possible. This historically meant until the US Navy could reinforce its defenses. Now with China’s anti access area denial strategy, this is becoming a less certain strategy.[1]

[0] https://www.nytimes.com/2017/11/04/world/asia/china-taiwan-m...

[1] https://thediplomat.com/2017/05/chinas-a2ad-challenge-in-the...