The puzzle is that the TPP does not appear to have maximized its leverage in the current legislature. The party's leaders turned down opportunities to grab the speaker or deputy speaker positions or to negotiate for cabinet positions in a Lai government, and over the last year they have instead prioritized opposition to the DPP administration rather than conditional cooperation with the ruling party. More surprising still, they have publicly aligned themselves with the KMT on many of that party's most controversial policy initiatives -- even when those policies are broadly unpopular.
This transformation of the TPP in the public eye from a centrist swing party to a "pan-blue subsidiary" has generated a widespread sense of angst and betrayal among pan-green commentators, who have accused the TPP of "subordinat[ing] itself blindly" and "march[ing] in lockstep with the KMT," and even tacitly cooperating with the CCP to oppose the DPP and the Lai administration. The TPP's public image has shifted so dramatically that many observers of Taiwan politics now simply assert that the legislature is "KMT-controlled."
The problem with this assertion is that it's wrong. The TPP legislative caucus is not actually marching in lockstep with the KMT on every issue, as I'll argue in what follows. On the contrary, it holds preferences that are quite distinct from the KMT, it has acted as a significant check on that party's legislative caucus, and its public cooperation with the KMT against the ruling DPP will be temporary and limited, rather than comprehensive and indefinite. But for their own reasons, neither the KMT nor the TPP want to advertise this fact. For the moment, they both would rather have everyone believe they are a unified pan-blue team cooperating to stop DPP overreach.
No other explanation is consistent with the political outcomes of the last 18 months.