In my opinion the reasons are:
1. TWICE music evolving: the girls went from cutesy which gave them their biggest hits ever in their career to more a mature sound so obviously the korean GP is not used neither seems to like it.
2. Choreos lacking of signature moves: We all know choreos help a lot with the performance of a song, if a choreo goes viral then the song will obviously. TT, Cheer Up, Fancy and more TWICE’s song with iconic dance steps were something people fell in love. I think their newest songs lack in that aspect, their choreos are getting harder and coordination as usual is incredible but the signature moves are gone.
3. New favorites girlgroups: This might sound stupid because many big and successful girlgroups can coexist together this not a competition, but i think korean GP moved to other girlgroups to find new sounds I guess? So TWICE niche is not into them anymore.
TWICE is growing so much international regardless and what some toxic stans call a “flop” is what many groups will wish to have.
This is just my honest opinion after observing their comebacks since Feel Special in 2019 (which is a big hit in Japan, Japanese have taste) till so far Alcohol-Free initial performance.