Oh put a pin in that because it's too goddamn precious
It's not explained, but it's emphasized again later that even if all of Soong's magics are performed exactly right, this just happens more often than not, and did in the process of creating Data and Lore too. So it's nothing specific to Lal. Why Data doesn't try again doesn't really get much more explanation than that either.
I always figured Data was just waiting until he had a more sure-fire way to prevent the breakdown before he tried again.