Because Riot doesn't have the budget, EMEA and NA still use the same studio as the league of legend, and that's telling. Both regions have no money for more matches. Remember, Valorant's esports is running at a loss, especially in the West. The game is definitely making money, but why should they spend more money to expand into bigger studios (And to the esports scene when it's just good enough as a game advertisement? )
Look how long it took them, actually, to fix their PC at EMEA. They had to accommodate the same staff and the same dogwater PC that runs both games. Now, tell me how they could end the season faster? With that shitty closed-in studio that has zero fans? Might as well make it online at that point.
It's just a straight-up scheduling conflict. LPL and VCT CN are completely separate stadiums, aka there's literally zero conflict, no matter how fast or how slow they do it (They still avoid it, but they don't run into the whole production issue). Pacific comes close, but it's vct kr with LCK for a reason.