Yeaaaahhhh, but you're thinking more about this from a Roller Coaster Tycoon aspect on sandbox mode. In reality, they're going to take into consideration things like existing infrastructure for electricity, water lines, and other logistics we're not aware of.
I'm not sure if you have kids, but being the father of a not-so-brave kindergartener, I can attest that small slides cater to a larger age range of kids who get bored quickly in lines rather than something like a more thrilling tornado. It doesn't take much more than a few slides for them to have a blast. Meanwhile, while the kids run around the adults can lounge around and slightly relax with a watchful eye nearby.