<p>I think one main reason is that some people just like a big environment. They like having lectures more than intimate classroom settings, they like big classes, lots of people, big cities, etc.
Also, sometimes universities are less expensive (this of course is not universally true and there’s certainly ways to go to LACs and pay less or go to universities and pay more, but in terms of big state schools, it’s often cheaper, especially in-state). Of course, there are small state schools, but sometimes those are less well known or prestigious.
Which brings us to another reason: more people in general known university names than LACs. Some people partly pick colleges based on name recognition. Bigger schools often have more name recognition. Many more people have heard of UCLA or Harvard over even very prestigious LACs like Amhearst or Wesleyan.
Also, just a side note: TAs may be hit or miss, but professors can be too. Professors are often more hits than misses, but there’s always those professors that do great research but can’t teach AT ALL–and in those cases it’d be nice to have a TA or two.</p>