a lack of investment in a second north/south runway by the airport owner because it costs more than and brings in less cash than a new carpark/terminal shops.
That's only because the airports are not penalised for being inefficient. If airports were held accountable for airborne/ground delays there'd be runways and aerobridges popping up everywhere. Brisbane got to 60 minute airborne delays in severe CAVOK before they even made mention of building a second runway. Even then it was only because they were publically shamed into taking action that something got done.