What's the appeal of shaka? Expansive isn't a very good trait. The UU is decent, but not really anything special. The UB is the only really good thing about him.
Are people voting for him because of how his AI can dominate?
I routinely say that expansive is underrated. Workers are an important part of REX, almost equal or maybe even equal with settlers from IMP. What good are settlers without improving tiles? Granaries allow even better synergy with REX, since you can put them up for half cost. Granaries go in every city, usually sooner rather than later, so fast granary = faster infrastructure in the city. These things alone make expansive quite solid in the early game, and that's one of the most important times in Civ 4. You're always going to use workers/granaries, so that is pretty versatile.
There's another bonus too though. In the mid game, while running HR, the happy cap is usually nullified. The main detriment to growth then becomes health, and + 2 often means an extra tile worked in every developed city. This is a cottage, mine, whatever. Can this match something like financial during the time period? Likely not, but it's not as far back as just looking at it face value implies. The early game may leave expansive in a stronger position than financial depending on map, and no matter what expansive is guaranteed to be useful.
The main appeal however is the UB. Cheap maintenance reductions are nice, but more importantly you're likely to use them anyway, meaning their opportunity cost is extremely low. Again, this is a major early game boost.
The UU is situational. It absolutely owns when the AI doesn't have metal or does not have it hooked up. Otherwise, it's a bit lackluster (though you can certainly reach deep to pillage metal if you know where the AI has it). Impi can annoy the AI pretty nicely though via pillaging, opening the door for later conquest.