This is likely due to law getting far more specific over the decades, with less room for interpretation.
Having followed a lot of the recent SCOTUS cases, I can say that if you think the law is leaving less room for interpretation nowadays, you are sorely mistaken. Look up the "Armed Career Criminal Act"--it's an example of what seems like it ought to be a simple matter of interpretation (look! it defines "violent felon"!) into a headache (okay, the person has to have committed a crime whose state-level common-law interpretation in 1984 had to have required at least this much force, and I'm sure I'm still missing some details there).
-Washington Post