This is a good question, I'm not sure why either. He is considered by Bill James to be the greatest second-baseman of all time. James used a "win-shares" formula to determine the greatest baseball players of all time - and if you look at his list, the formula is rather convincing. Overall, he has Collins as the 12th best player of all time.
Personally, I think Hornsby was - and I think Joe Morgan is the most overrated 2b of all time.....but that's just me. I also think Hank Aaron is one of the most underrated players of all time.
Regardless, Collins WAS definitively better than Nap Lajoie and yet the hobby does not reflect that.
Found a cool site:
http://baseballguru.com/egartman/ana...gartman01.html