Here in my area of NY I've been noticing the same thing over the last few years. there are definitely less deer than there were 10 years ago thanks to the liberal doe permits issued every year. I'm no expert by any means but there are some changes that have occurred that I think may account for what I'm seeing.
First, there simply just aren't as many hunters as there use to be. That doesn't explain the lack of sightings during bow, but it definitely has an impact on sightings during our gun season. it use to be that groups would organize drives all season long and keep deer moving. I just don't see them any more.
Second, land use has changed. More and more of the land around us is being sub divided and developed. around here you need 5 acres to zone for a septic field. That usually leaves 4 acres of undeveloped, yet heavily posted, property for the deer to hunker down on. after the first couple of days the dumb ones are dead and the survivors only move when kicked.
third, the land that is being hunted is tightly controlled by a small number of hunters and managed specifically for hunting. That means they plant food plots to hold the deer and try to hunt "low impact" so as to hold the deer on their property.
Granted, that's just my take on it locally, but I still see the same number of deer hit in the roads as I use to and large herds in cut fields after the season, so the deer are "somewhere", just not where I tend to be.