Is it? 39 libraries that are 35 lines of code each or just define a bunch of functions that your code can then call optionally may well not take that long to parse. How many gems does the typical Rails application use? Libraries are the equivalent on the web, only someone else doesn't resolve the dependencies; you have to include the dependencies manually. Is it that surprising that people are using a variety of helper libraries to do ads, analytics, DOM manipulation, etc, etc? That's fairly standard for development.
I think saying we're “drowning in JavaScript” because we've gotten a lot better at modularizing our code instead of copy-pasting it from everywhere seems like lamenting the wrong part of the problem by far. I would rather every site include Google Analytics, DoubleClick, jQuery, and 10 jQuery UI plugins than be subjected to the cascade of security and functionality bugs folks would run into if everyone was trying to roll their own solution for everything. There are already enough with the use of common code.
Using libraries for third party code is good, and the fact that we're doing it is a step forward, not a step back. Now, there may be room for folks to choose the third party code more wisely, but that's a perennial problem when you're willing to use code that's already been written.