Descent was great (I love Descent 3) but other than that there is only Forsaken, why has noone ever made a modern game like that? I think its a shame :)

Its unfortunatly a niche that not many people enjoy playing. Shattered Horizon is similar in that there is no such thing as up or down. It has a very small community with only a few servers with anyone ever on them though.

It's a hard game to master and even to get the hang of so most people being lazy will tend to flock to games like UT nad Quake.

Also Descent 1/2 sold a combined 500,000+ copies while Descent 3 only sold about 25, 000 copies. Freespace 2 only sold some 23, 000 copies. Hence why there hasn't been a new version.
Check out Miner Wars.

Didn't Prey use Descent style controls for the vehicles rather successfully?
Of course, Prey wasn't a big success either, even though I personally loved it.
But I can understand why it isn't common any more, as most games are developed for consoles first later to be ported to PC - Descent style 360DOF games control terribly with gamepads, at least those I have tried.
arcade flight sim stuff work pretty well since there the planes level when you let go of the analog sticks, but stuff like that doesn't work as well in games where there is no correct up or down.
I don't know how they worked out the controls for the console version of Prey though, might have worked fine there.

Games like Descent don't succeed much anymore because well frankly people are lazey and want the easy to learn games. They think that they are fun and worth while because they can master them in less then a few hours of play.
However teh ones that have played it and still abandoned it, will still tell you that Descent series was a fun game and very cool. Descent is also one of the top 5 games of all time. It is out right amazing that people still play it. I am one of them.

www.minerwars.com
Does look like Descent don't you think?

I was a decent Descent player (heh), I played using joystick.. and I remember no one was impressed when I showed them. They said it was too confusing. Meek :D
Anyway that was the time vertigo from playing 3D shooter was an issue, so I agree: why no one makes this kind of game nowadays? when vertigo is no longer an issue that is

Shattered Horizon is probably the only 6DOF game I can think of that's been released recently.
http://www.gametrailers.com/video/raid-on-shattered-horizon/58508

Here's a Doom 3 TC called "Into Cerberon". It hasn't moved from alpha v0.04 for two years now, but last month they posted a news item that they moved to a new server. It's basically a Descent recreation.
http://www.chmodoplusr.com/IntoCerberon/