HELP! - Synoptic Problem Research Question

Whether serendipitous or not, I stumbled from the Synagogue article into the Synoptic Problem article a week ago while reading IVP's Dictionary of Jesus and the Gospels. Perhaps as a dog returns to its vomit, I was reading through it again tonight. But unless I'm missing something, this explanation seemed lacking, about the problems with Lessing (1776) & Eichhorn's (1796) hypotheses of an early Gospel in Aramaic:

"The main problem with this argument is that as one sought to reconstruct what this Ur-Gospel looked like, it began to look more and more like an Ur-Markus... This in turn began to look more and more like the canonical Gospel of Mark."

I get the point there at the end, but can anyone tell me why the reconstruction trended that way? I mean, especially since they're positing Aramaic instead of Greek, why didn't they simply posit a giant sized Gospel with everything found in all three Synoptics? Seriously, was that just too easy, or were there deemed to be some particular problems with it?

For scholarship as old as America, I'll print your name here in lights with much fanfare if you've got the true scoop!