Thanks for the all the points raised here. It has been very enlightening to read all your replies.
My "new" conclusion is YES, THERE IS A POINT IN U2 MAKING A NEW ALBUM.
They wouldn't want to end their album-recording career with the dud that is No Line In The Horizon, right?
Perhaps that is their driving force. They want to end their career in their own terms.
And just maybe, if they can have faith and confidence in their next album, and they can properly announce it to the world before release that it will be their last studio album - they can get some sales and awards for that.
That would be icing in the cake for their legacy.