Because the VN ending is better and you should play it. The ending to this still got to me and it wasn't awful, it wasn't great, but it wasn't awful.
There's like 20 endings in the game so good luck on getting Taiga's
It's 6 weeks, and it makes literally zero sense logically (seeing as she doesn't talk to Ryuuji even once during the 6 weeks), but makes decent sense thematically. It's her "graduating" from relying on Ryuuji for every little thing.