Let's start with the circus, because that's just way more fun. In the part of the story set in the 1930s, the setting is vivid and colorful; whatever is faults may be, there's light, life, and color in the circus. And it's not easy to miss.
When Jacob first gets to the circus, he is astounded:
I peer inside. The tent is enormous, as tall as the sky and supported by long, straight poles jutting at various angles. The canvas is taut and nearly translucent – sunlight filters through the material and seams, illuminating the largest candy stand of all. It's smack in the center of the menagerie, under rays of glorious light, surrounded by banners advertising sarsaparilla, Cracker Jack, and frozen custard. (3.113)
Jacob sees the circus as a place of heightened, exaggerated excitement. It is "enormous," full of "sunlight" and "illuminati[on]," and its big tent is full of "rays of glorious light." Note all the light imagery here. Everything is bright, clear, and full of promise. But this is just Jacob's first impression. Supporting all that light and glory is the cold, hard idea of commerce. The whole purpose of all this light and glory is to bring in money.
And don't forget, the circus isn't permanent. It goes up and comes down easily, sometimes within mere hours, and travels by train from place to place. The circus people don't have a permanent home. They go where the circus goes, all across America.
The other important thing to consider about the 1930s setting is what was happening in America: it was the beginning of the Great Depression. For Americans suffering through the worst economic crisis the country had ever gone through – with little money and food to go around – attending a circus performance would have seemed like a wondrous, desperately needed escape. Going to the circus would have been a longed-for, much appreciated break for those who could afford the tickets. Think about it. These people didn't have TVs. They had little entertainment and no travel budgets. Plus, they had to wait for the circus to come to them – they couldn't travel to see it.
It was also Prohibition (1920-1933), a time when people weren't legally allowed to drink alcohol. The laws that kept Prohibition in place didn't keep people from drinking, though. They just had to drink on their own terms, which usually meant smuggling liquor in from other countries, making their own versions of liquor (moonshine), or drinking the nasty substitutes available on the black market, like jake (which is what paralyzes Camel). Because they couldn't use liquor as an escape, people were even more likely to turn to circuses for entertainment.
In contrast to the circus, the nursing home is all too permanent. If the circus had an excess of movement, the nursing home has too little. Within the home, Jacob is led from small room to small room, not even under his own command. It takes all of Jacob's guts and courage to walk out of the home and into the world, much like it took all of his guts and courage to leap from circus car to circus car in the middle of the night with a knife in his teeth and murder on his mind.