Converting 2D movies to 3D worthwhile?

2D to 3D?

There were several 3D movies released before Avatar that didn’t fare so well in theatres: Chicken Little, Up, Polar Express and A Christmas Carol to name a few  – but only after Avatar became the highest grossing movie of all time were 3D films considered financially successful. Avatar however, was the only successful film shot in 3D using live actors. 

So if 90% of all 3D films before Avatar weren’t successful, either financially or critically, then why are we hearing about so many 3D conversion film treatments every couple of days? Why are studios so excited over converting films to 3D so quickly just because one film made boat loads of money?

Is it any different from adding colour to a black and white film? Is it worth the money?

Colourised and non-colourised Robin Hood