Because anything planted there would end up a casualty to foot/bike/dog/car traffic. All that hard work walked, rolled, or peed on. Salty snow banks piled on etc.

As a matter of fact, the hellstrips (aka parkway strips) are almost always landscaped. And the landscape solution that is used the greatest majority of the time is turf, since the space itself is generally used for moving about or there is such activity in the vicinity. It makes sense to landscape it in such a way that people can walk on it--like carpet--and that there are not obstructions present to get in one's way or themselves be damaged (as frankielynn points out.) While turf is generally a good solution, it requires maintenance. Sometimes people choose to pave these spaces and have only a wide sidewalk.

I personally detest those little hell strips. Takes waaaay too much water to keep sod looking nice there .... which in these days is not water-wise IMO.

I've tried to get my hell strip sod to die by ignoring it for 2 years now. No luck. Looks crummy, but just won't die so I can plant something else there without too much sod removal/digging/hard work! I think there are a lot of choices for these spaces that would withstand the elements, though I've never seen people walk on them here in Texas, so don't think they need to withstand foot traffic. Jasmine, lirope, mondo grass all come to mind. Not fancy, but drought tough once established.

I've also heard of many HOAs who require that sod be in these spaces. Crazy, in my mind, but true. :)

"...though I've never seen people walk on them here in Texas, so don't think they need to withstand foot traffic." People don't walk on them in lieu of the sidewalk. They walk on them going to the mail box, to the car, cutting corners, crossing the street, etc. Vehicles decimate these strips at some intersections.

"Jasmine, lirope, mondo grass all come to mind." When mature, many Liriopes have no trouble reaching 18" - 24" height, which would be an impediment to getting into or out of a car that was parked at the street. Also, it creates a visual barrier to the sidewalk. After being stepped on a few times, Liriope becomes quite unattractive (as I've seen around Atlanta too many times.) Too unfriendly looking insofar as accessing a sidewalk from the street IMO. I could see dwarf Mondo working IF the site was able to satisfy its cultural conditions and the traffic load wasn't much.

I was thinking more like a few trees and stones. There is a neighborhood of Victorian homes and they are lined with huge trees in that strip and maybe it's a rule there since there's a few little young ones in places where there were none - they mostly have nice full landscaping up to the sidewalk too.

Most out here never walk on that bit either except once in awhile, since there is always a connecting paved strip for each house, yet it's 3 ft. wide and just plain old grass.

Kitteh - we have the little connecting strips too ... and of course the driveway is available in many homes to park in for visitors. For myself, I am not so willing to sacrifice scarce water so that I can have a daily grass-filled parkway strip for the occasional times that visitors might need to step on it. But that's just me - but I'm in a very hot, drought-prone part of the country, which informs my opinions.

Stones are a thought, but they, too, would be hot - especially around trees, depending on where you live. Folks here often plant spring flowering bulbs in the hellstrip, and keep it covered with mulch and/or organic stuff during the rest of the year. In my neighborhood, we have generally two parkway trees for every lot, though I've seen crepe myrtles line the parkway to a nice effect.

My two cent's anyway. :)

The tree-lined street is actually very cool in the summer. I love crepe myrtles and if they got bigger they might provide shade for stones and a few rock plants there.

I've seen on Pinterest where people turned those areas into little rockeries with pots of herbs and heat tolerant plants.

I live in an area of the country ( San Francisco area) where the houses are set pretty close together and there can be little front yard space.
These hellstrips are considered a valuable landscaping commodity in many neighborhoods and have sparked some of the most unique plantscaping vignettes in the city.
People have planted vegetable gardens, succulent gardens, rose gardens, rockeries and full on topiary gardens.

this photo is from landscape designer David Feix's Flickr page . He's done some beautiful hellstrip planting schemes. This one uses all drought tolerant plants that have great color and textural contrast.