Cheaper to operate, which over an entire city's worth of street lamps is very material. Sodium-vapor lights eventually need to be replaced (as do LEDs), so why not replace them with a modern technology that's cheaper to operate?
I'd imagine some LED luminaries are consuming more energy than the sodium lamp they replaced, as they are usually brighter and some will have terribly inefficient power supplies.
I’ve seen in a number of places where the led lights have rapidly degraded, putting out really unpleasant bluish, purplish hues, as if the super bright daytime like sports field lighting everywhere wasn’t already bad enough. So this rapid degradation necessitating replacement no doubt eats into some of the cost savings.
Also, “cheaper to operate” mostly seems to have turned into “pump out more photons” instead banking the savings and maintaining nighttime lighting at non eyeball scorching levels.
https://fee.org/articles/why-are-some-us-street-lights-turni...
I’ve had issues with household LEDs that needed replacing well before expected lifespan.
I also saw this article some time back discussing issues with LEDs. https://nymag.com/strategist/article/led-light-bulbs-investi...
I’m not against LEDs, but the usage and implementation in a lot of cases to date could be better.