It's just that in Europe the data is much more sparse to begin with. In many places Google didn't go multiple times, so there just can't be older data. On some streets however I see that if the data was really old (before ~2010/2012) Google probably decided that the quality was so bad – well, it really is – that they do not make it available. So even if there were multiple passes it is not a must that this feature comes available.
It's just that in Europe the data is much more sparse to begin with. In many places Google didn't go multiple times, so there just can't be older data. On some streets however I see that if the data was really old (before ~2010/2012) Google probably decided that the quality was so bad – well, it really is – that they do not make it available. So even if there were multiple passes it is not a must that this feature comes available.