After WWII, Germany lost a large section of their Eastern Territory to Poland, and everyone from there was resettled within the new German borders. Those people were furious, and as a result German policy was to demand that territory back, and a refusal to recognize the new borders. A couple decades later a lot of the people who grew up there had died of old age, and the new generation had no relation to the old territory. As a result public sentiment changed, and Germany publicly recognized the new borders when it was politically advantageous.

Taiwan is probably going through the same process, just a bit slower since it's not just about territory but about national identity. Each generation weakens the ties to the old "Chinese" identity and strengthens a "Taiwanese" identity, until a tipping point is reached.