I honestly think it's more that Steve isn't bursting with crestivity when it comes to Maiden material like he was when he was younger. He has British Lion to scratch his musical itch (and their output isn't all that high either). Bruce has his little project and Adrian has one too.
They probably do have enough left in them to produce a solid Maiden album, but if they're not brimming with enough ideas, no point in flying everyone from around the world to try and force out a new album just because.
I suspect that's been the case with the last two albums too. A bit of a creative drought, followed by a short intense period of creativity where they suddenly ended up with a LOT of material to cram into one album. Steve's 'epic to end all epics' bids like Red and the Black, and Hell On Earth, while Bruce was clearly massively into Empire of the Clouds (obsessively so, maybe!) and maybe Darkest Hour, too, another of his pet obsessions. Writing on the Wall was quite a new look for Maiden too that smacks of sudden inspiration.