You should look at the source for that chart. Not sure why grid.news decided to do this, but the original chart[0] actually has 7 categories. grid.news left some of those out and (combined?) some others? Anyways I think the full data tells a pretty different story...

There does seem to be recent (~2018) in support for independence. But the interesting thing is there was actually a shift towards more support for unification right before that. It's also probably important to take into account the methodology[1] and the low sample sizes corresponding with the largest shifts

[0]: https://esc.nccu.edu.tw/PageDoc/Detail?fid=7801&id=6963

[1]: https://esc.nccu.edu.tw/upload/44/doc/6965/%E9%87%8D%E8%A6%8...

The original chart https://esc.nccu.edu.tw/upload/44/doc/6963/Tondu202206.jpg shows even more the movement away from unification with China.

The lack of support for "Full Independence" rather than the Status Quo of effective independence they have now is usually explained by people not choosing a policy that provokes China into attack.

That’s exactly it. There’s interviews with the the president saying effectively that. A reporter tried to get her to say it on record, and she effectively said there’s no need. They de facto independence. No need to provoke an attack