They didn't indeed. And you know why? There was a big discussion, between the fraction that said you have to spell out the most important rights so that nobody would think that it's ok to violate them, and the one that said "we already said the government has this set of very restricted functions, if we start spelling out the specific rights, people would think these are the only rights that should be protected, and others are not important and the government is OK to expand their function and violate those rights, just because we didn't include them in the list! We can't have that!" After a while, it ended up looking like it does now.

Of course, both of them turned out to be wrong. Not only people think that rights that are not explicitly enumerated do not deserve protection, not only the idea of limited government bound by constitutional limits is completely dead and buried, now people think that explicitly named rights too can be violated at will. Maybe because they have been spelled out a bit later, so they can't be that important. After all, First Amendment isn't something that's very important, that's why they made it the first one. Like the trial one, we'll do some silly stuff first, to warm up, and then we'll get to really important things.