They're also significantly more efficient with the light given out, directing nearly all of the light down. @James explained this well.

Keep in mind that most LED streetlights uses lens optics, which causes them to be superglaring, compared to HID and LPS optics.

That's only a problem with very poor placement/design of the lighting installation. I have strict requirements I need to abide by when I design with anything, particularly LED's to avoid glare. Also, glare is a very subjective, one looks like glare to one person is fine for another.

Glare seems to be tied strongly with luminaire design and positioning as part of the lighting layout. A poorly designed lighting layout with low cost badly designed luminaires will have a lot of glare.

I wonder why electronic gear for low pressure sodium never took off the same way it did for fluorescent. The gain in system efficiency would have been quite nice to have. I know they existed for lower wattage lamps but I don't believe a full range of wattages was offered, nor any for the North American market to my knowledge.

Then again, low pressure sodium gear in North American countries remained the old style leak transformer design until the very end. System efficiency suffered, with the lower wattages, a 18w SOX system here with a leak transformer draws close to 40w in total power consumption. 

Due to our low voltage, we never really got the choke + ignitor style setups, even for higher voltage circuits. Ironically due to rarity of the correct gear, some collectors in North America use standard electronic fluorescent gear to run low pressure sodium lamps.

I think that by the time electronic SOX gear was taking off, main road SOX in the UK was being phased out, SOX just lasted longer on minor roads, and thus saw electronic gear. That's my theory anyway.

The electronic ballasts for SOX are not only possible, but would be superior to the magnetic mainly in the efficiency (of both ballast and the lamp) and low weight (allowing more of the weight/mast loading budget to at least a bit more efficient optics).
But that technology came too late to the party. In the meantime HPS began entering the 150lm/W game, with way smaller burner, so allowing more efficient optics, so much the overall system efficiency became practically the same. And still without any electronics beside the ignitor. And for way lower material costs, from lanterns to replacement lamps.
When electronic became reliable and inexpensive enough to be used in the wild for the, the LEDs became somewhat viable, reaching efficacy, reliability and overall price to be competitive, with the high color rendering as a bonus. And there are we today.

Someone may wonder why such focus on the cost, but what else the zero CRI orange can offer than the lowest cost of light? It was prcisely the "how to get the cheapest light", what was behind all its development and why it is the thing at all. The only reason for LPS to exist is to get the light cheap.
And there it is just losing to the newer technologies, initially to HPS (similar or only slightly lower efficacy, but way cheaper to procure and maintain), then recently to LEDs (similar or even higher system efficacy, but way better optical control and most important nothing of that lost with lower power packages, allowing installations with less light waste so even less power requirements)

Yeah that was what I thought too. It's the same thing with electronic HID ballasts. They saw some limited use for example indoor CMH systems where the other advantages of electronic such as reduced flicker was desired, horticultural lighting where the ability to tune the lamp power and run multiple lamp types was advantageous.

Interestingly enough some electronic HPS systems for roadway lighting existed too. Toronto tried them on a limited basis and NYC converted a lot of their streetlights to electronic HPS in the late 2000s/early 2010s. Unfortunately they came fairly late and most of those lights already got wiped out by LED. 

Here in Israel, electronic HID ballasts were used only indoors in tracklights mainly.
And I've seen LED lanterns with inferior optics compared to HPS lanterns.