Interesting that in the 2007 Master Plan, the forecast passenger total for 2030 was 27.2 million - how things have changed!
Going from unrealistic optimism, to a healthy dose of reality. Back in 2007 the new runway at LHR was not seriously on the table, HS2 wasn't a reality, and MAN hadn't come close to becoming the global hub that it now is. I think there is a realisation that the effect of HS2 will be to draw passengers towards LHR, rather than the reverse effect of enabling BHX to effectively become LHR's third runway.
Of course, politically, not going for massive expansion and a 2nd runway makes it far easier to get past the NIMBY councillors sat in Solihull too!