It's the acqueduct that kills it. And it's not all that great of a wonder. +1 health is pretty minor considering that a granary plus all grain resources gives you +6 total, +1 population is no big deal either considering the average growth rate of a city. How fast do your cities take to grow back 1 pop after a whip? Not so long.
The only reason I ever really want it is for the GPP, if you have stone then you may already have the 'mids so the HG completes the set, so to speak.
Growing time is underrated. It's the infinitesimal argument: it feels like I just have to wait a few turns, and a few turns of costing virtually nothing sums up to nothing.
A similar analogy is anarchy, you wait one turn, but the empire cost is often pretty large.
Due to slavery, we're accustomed to be view regrowing as a small cost, but from turn 100 to 150, 10 turns is a very long time.
Some people measure the value of hanging gardens by worst case whipping the one population across the whole empire. What you can do with one extra population is a big problem for the following reasons:
1) you often lack extra happiness due to going early mathematics (except ottomans)
2) with your available happiness you probably can and are working the really good tiles (specials, riverside cottages, riverside mines).
2b) so you probably end up on a non-riverside cottage, a coastal, or worse an unhappy citizen.
3) you may not have so many cities, each of which increase the total bonus, due to the economic impact and having to get hanging gardens fast.
On the other hand, if you have a lot of food, one extra population means you can start running a lot of specialists (if you had code of laws in addition to mathematics) that much sooner.
Maybe it's best to think about the total food increase hanging gardens gives to your empire.