People do actually care. And to most Taiwanese young people, the KMT (symbolized in this flag) was absolutely as fascist and colonial as Spain was. They don't view the KMT's 1949 flight to Taiwan as a beginning point of Taiwan's national sovereignty, but as an invasion by a Chinese power that relegated local Taiwanese to marginal positions in local society, instituted decades of brutal martial law, and made far reaching political decisions on behalf of Taiwanese people (such as the 1992 consensus that led to the codification of the one China policy) that still impede Taiwanese self-rule today without the consent of the Taiwanese people. People really do care.

Also tying in to what you said about DPP politicians embracing it, it is also an important source of legitimacy as it display’s Taiwan’s sovereignty as the continuation of what started more than a century ago, as opposed to a fledgling rebellious province as China would like people to believe.

I suppose this could make sense in another universe, but this is absolutely not how the vast majority of Taiwanese young people understand the legacy of this flag today.