One day my mother sat me down and explained that I couldn't become an explorer because everything in the world had already been discovered. (Prologue.3)
Jacob's mother stifles his imagination by telling him this, and it makes him miserable and depressed to be in the real world. As we later learn, there are still parts of the world to be discovered, at least for the majority of normal humankind.
As for life on the island, little has changed. (2.105)
Miss Peregrine's letter is subtle, to say the least. "Little has changed" not just because they're isolated on an island, but because they're isolated in time.
"All I can say is they weren't your regular sort of orphan children." (4.102)
The orphanage is separate from the rest of the island, away from the village and pretty difficult to get to. They want to be apart from everyone else to keep anyone from finding out their secrets.
I thought about how my grandfather's family had been taken from him, and how because of that my dad grew up feeling like he didn't have a dad, and now I had acute stress and nightmares and was sitting all alone in a falling-down house and crying hot, stupid tears all over my shirt. (5.20)
Seems like this feeling of being alone runs in the family, and it's reached a critical mass in Jacob as he thinks about how his grandfather was alone, and his father felt alone, and he feels alone. That would be hard to deal with even if he wasn't in the middle of a creepy falling-apart house.
There never was any girl. I'd imagined her, and the rest of them, too. (5.72)
Jacob sometimes thinks his isolation is driving him crazy enough to see things. At first, that's a more rational explanation than the fact that some kids might be invisible or able to shoot fire from their hands.
"There was a time when we could mix openly with common folk. […] But the larger world turned against us long ago." (6.91)
The time loop isolation isn't entirely self-imposed—the real world kind of wanted them gone, too. At least that's what it feels like when they start murdering peculiar-kind.
"We were always so desperate for news of Abe. I asked him once if he should like to worry me to death, the way he insisted on living in the open like that." (6.64)
One drawback to being stuck in the time loop is that it's difficult to communicate with the outside world. Even if Grandpa did want to communicate with them, it would be hard to get news to them.
When there was no light anywhere but [Emma's] face on my little screen, I lay there in the dark, still looking. (7.201)
Thanks to modern technology (that doesn't exist in 1940), Jacob is able to see Emma even while he's apart from her and feeling lonely. We bet if he took her picture for real, it would disintegrate outside the time loop.
"They don't know where to find us. That and they can't enter loops. So we're safe on the island—but we can't leave." (9.8)
Here's another drawback to the time loop: It's like the hotel California. You can check in any time you like, but you can never leave. At least the amenities are nice.
For his many sacrifices, he received only scorn and suspicion from those he loved. (9.69)
This is perhaps the most tragic part of Grandpa's death: He lived a basically selfless existence, but no one around him seemed to appreciate it. In fact, they shunned him because of it. Tough break, Gramps.