Because market access is not the reason they're banning it. It wouldn't be very believable to now act like it's about a different issue than national security. You'd basically be saying "if you give us market access, then we'll let you spy on our citizens."
In a democracy you get the types of discussions that we've been seeing about TikTok, so that door's shut now. This sort of "trickery" only really works for authoritarian countries, where the discourse is exclusively behind doors.
