Why are people so persistent that Taiwan isnt a country?

Each time I get in a conversation about ethnic background, or anything about Taiwan, I would always get in the topic of “is taiwan its’ own country?”. Taiwan gained its independence from China long ago. Taiwan is its own country!!! why is it that people just cant get that? my friends often say, oh, taiwan is part of China isnt it? i get so pissed. why is it that people are brainwashed, (or whatever you call it) into the thought that taiwan is not its own country?