I've had a 3-9 SWFA on a .308 for years and don't see it ever getting replaced. That said, I likely would not buy one today.

For hunting a 3-9x would do most anyone just fine. I prefer a little more magnification at the bench, so I like 4-16 or 4.5-14x.

On my centerfire rifles I have:
Three 3x9
One 3.5-10
Two 2-7
One 1.75-6

I used a 3-9 opening weekend. It still works.

I think a lot of the reason more high magnification scopes are coming out is the increase in the long distance and precision rounds. Seems like every other rifle on the shelf is a 6.5 creed, and is bought by some dude with aspirations of making a 1000 yard shot.

A second reason is technology improvements in the lens making process. In years past there was only a handful of manufacturers that would get into the high powered optics. Now it seems like quality glass is being produced by a dozen different mfgs.

So to answer the OP, 3-9 scopes are still sold, and still arguably the best all-around for hunting. But they just aren't the new and flashy products to put in the front of the display case.