daylighteclipsed Answer:

And isn’t it interesting that in both cases Bill was involved, especially after Alex said how much Bill is trying to break Dipper’s spirit?

See I’m not convinced Mabel had total control over the place like she thought. After she starts wanting to leave, it takes on a mind of its own and tries to stop her. ‘Her creations’ turn on her and start attacking her and Dipper and co. Mabel loses the ability to manipulate/create more things in ‘her world’, meaning it was never really ‘her world’ to begin with. It’s always been a trap designed by Bill.

Bill gave her the illusion of control, but she never actually had any. Mabel herself even says the place gives you what you want before you know you want it. That doesn’t make any sense, unless it’s not really what Mabel wants but it makes her happy enough to believe it’s what she wants.

I think Bill took what Mabel wanted and exaggerated her desires. Mabel was hurt by Dipper. She wanted a brother that was supportive and wouldn’t leave her for supernatural mysteries. Bill gave her that, but amplified. He gave Mabel someone Mabel didn’t exactly want, but could have fun and forget about reality with.

And someone that would inevitably completely break Dipper’s heart if Dipper so managed to reach Mabel’s bubble. Bill wanted Dippy-Fresh to make Dipper hurt and angry enough to give up on Mabel and storm off, like how Dipper temporarily stormed off in Dreamscapers when he was convinced Stan hated him. I’m like 90% sure Bill had a hand in the memory Dipper stumbled across then too; he wanted Dipper to give up and abandon Stan. But Dipper didn’t. He didn’t give up on Mabel either.

In fact, in Mabel’s prison, Dipper didn’t even express any anger toward Mabel about Dippy-Fresh whatsoever. Although I’m absolutely positive it had to feel like a literal knife was being twisted in his heart. Dipper hated Dippy-Fresh and Mabel’s friendship with him. He pretty much wanted to kill the guy. But Dipper was bracing himself for this. He knew before entering the bubble that Mabel was hurt by him, and that it was a prison designed by Bill. He didn’t know exactly what was inside, but he knew it was gonna be rough and it was. Bill tried to break Dipper’s spirit with hurt, anger, guilt, and insecurity (Dipper’s not cool and adored) in the form of Dippy-Fresh. But it didn’t work.

And Dipper tells you why: because he knows his sister. He knows she’s scared and that none of this–including Dippy-Fresh–is what she really wants. Dipper forces Mabel to stop lying to herself and living in denial and face reality. He recognizes that he was also lying to himself about wanting to stay in Gravity Falls to be Ford’s apprentice. He doesn’t give that opportunity up for Mabel. He straight up tells her it’s not what he wants. He doesn’t want to be cooped up in a lab with Ford all day. He wants to be with her (and if Ford had paid attention to the kid, he’d know that’s why Dipper was hesitating to take the apprenticeship in the first place).

Dipper was making his own choice, free of Mabel and Ford. That becomes certain when Mabel says Dipper can stay with Ford if he wants and, despite Mabel being safe now, Dipper still reinforces it’s not what he wants. Dipper wants to grow up with Mabel. That’s his desire and no one else’s.

Dipper has the will of titanium that could withstand Bill’s most diabolical trap, and the strength of that determination is drawn from how much he loves. I’m so incredibly proud of this young sweet boy for being his own person and never giving up.