courthouses look at it like this, they come along at the same time as other buildings such as markets or grocers- quite a lot of time your cities arn't even developed enough to have all of the basics in by the time they come around.
Now say a city is raking in 10 gpt, which would increase on every pop growth by 2 gpt while it also has maintenance costs of 2 gpt increasing by 1 every 2 pops.
1 pop = 10 gpt -1 maintenance
2 pop 12 gpt -1 maintenance
3 pop 14 gpt -2 maintenance
4 pop 16 gpt -2 maintenance
5 pop 18 gpt -3 maintenance
would you rather build something that increases the gold output so infact what your getting is this.
1 pop= 12 gpt -1 maintenance
2 pop 15 gpt -1 maintenance
3 pop= 17/18 gpt - 2 maintenance
4 pop= 20 gpt -2 maintenance
5 pop 21/22 gpt - 3 maintenance.
or a building that just reduces costs by 1 or so every turn, i appreciate this isnt exactly how maintenance costs work but its a good indication of what a building for only 30 more shields can do compared to a building without one, i dont normally end up building courthouses until well into the 1000's ad, as other builds get prioritised over it.
the other benefit to building/popping the taj is that we can use the resulting GA to fast build versailles if need be...