I don't know why, but 2^32 search space is WAY too small. Anything they could enumerate back then (or even today) is way too small. This is like saying they tried four times before they found a vulnerable one.

LCG generators like lrand48 have been understood well enough you could possibly calculate "realistic looking timestamp" input seeds based on intended output characteristics.

Now, do we think that's likely? Probably no more likely than then being "easily broken" for decades without being noticed by the academic cryptography community.