The big schools offer two things...

Legitimately, they offer one-stop-shopping for an approximate price. They may also offer employment as a CFI, but often this a sham since they hire ALL graduates you just end up sitting around all month with no pay to maybe do one disco flight...

Not-so-legitimately, they offer the ILLUSION of a large, well-funded, well-organized professional institution that OBVIOUSLY provides a better product than that little school based in the trailer on the far side of the home patch. Students (and their parents) are often totally clueless about aviation and don't realize that for 1/3 the cost the guy in the trailer can get the same (or better) job done ...not to mention his brother flies for FDX and will walk your sh*t in when the time comes...