Mannimarco would like to dispute that by being a lich you cannot ascend, as he makes daily rounds to Arkay to shoot the bird in his face. But then again, true ascension is what the dwemer tried, CHIM, and blah mentioned in the Loveletters.
Also, you need to peer inside the mind of someone whose considering lichhood. Some do it for power, some do it for continuing research (death is really a [censored] when it comes to that), you need to make sure someone doesn't get a hold of item X and burying it is out of the question, or making sure a bunch of daedra are sealed away.
Mannimarco is the only intelligent person that accomplished Lichdom with favorable results. Concerning his nature and his actions in Oblivion, I'd say he's already accomplished a hell of a lot against Arkay.
Becoming a constellation or whatever celestial entity he turned into is no easy feat.
The wannabe lich from the DB quest seems like the average aspirant. He's narrow-minded, egotistical, dying for revenge/conquest, and ready to lay down as Mannimarco's doormat.
I wonder why N'Gasta didn't attempt it though.