[chiph]

I don't have any concrete evidence, but my guess is that having the repeating value (the TLD) at the front meant that storing domain names in a hashtable was inefficient. Lookups would be faster if the more-unique part was at the front of the string, since the string comparisons would run faster.

[FlyingAvatar]

Wouldn't this make sense only if you weren't using a hashtable, i.e. a list or something else that had to be traversed?

[scaramanga]

such as a trie/patricia