Because you're still working on the first part. It's the same storyline, the EC mask is just required to continue it past a certain point. See the Stories Tiers and Rewards thread for more information.
I believe if you already selected "Go home" at the end of the first part then you can't continue to the vip section.
Not true, you can. & what hailey said is likely the issue because she seems to have less drops than the non vip mask requires to complete.
If you already ended the story but someone gifted you the 99ec story pass, will you still be able to continue that pass?