Newer build developments definitely bury the lines, like you would see in Sun Belt tract housing developments.
The thing is, when you do it up front, it then becomes cheaper to do it for everyone at the same time. Up here, we have loads of legacy housing (my house is from 1926, for example, and not the oldest on the street), which is all strung together with a hodgepodge of wiring. You'll often see two poles right next to each other, and older shorter one, and a new taller one with more wiring (and unlit fiber runs, but that's loooong PB post I don't have time to write).
So to bury the lines, you'll have to redo every individual home's electrical entry point, do a full street at a time, and do it over years and years. It would be a monumental undertaking for small towns, which is essentially what CT is, excepting a few larger towns and smaller cities (Bridgeport is the largest in the state, and still under 200k).
Also I believe that the state has granted the monopoly to a few players. We have one town, Wallingford, that somehow built their own electrical grid in the late 19th century, and through incremental upgrades, was able ot weather this storm with very few issues.
There's also the issue of ground freeze, we'd need to dig some deep-ass trenches to bury conduit on account of frost heaves and whatnot, and the soil up here isn't exactly conducive to that. When they did my sprinkler system, which needed to go down exactly 2", they needed a carbide tipped street saw to get that far down.
But then we piss and moan about power going out, and say "well it's only happened once this year", and talk ourselves out of doing it.
And frankly, it's worse in the winter if you're far form the main thoroughfares. Ice in the evergreen trees adds twice the weight, and branches from those go down and take out power consistently in the winter months. My parents house had a near miss in the mid-90's when an ice storm took off a 70' section and it dropped in the backyard 5 feet from the back door.
Sorry for the rant, this is just something that's been going on so long and is frustrating as my job depends on the availability of electricity, and I've experienced both this and Sandy and deal with CL&P often enough as a result.