Much like the coming storage update OSRS gold is becoming to POHs
No point in having a bigger team if you can not get shit from the doorway. Dude it's such fun content too, I have done like 50 on my ironman and actually enjoyed it. Im half certain they had a lot of it devved before poll. Which honestly is rather debatable. I wish they'd do the vast majority of the work following the survey so they don't waste any job. Warding vietnam flashbacks kicking in.
Mahogany Homes was created in a closed environment with a single Jmod, once it passed on the polls a group went to actually work on implementing it. When you look at Mahogany Homes it is not a hell of a good deal of work behind it, only requiring a couple of new versions, apart from that it's reusing assets they have needed for awhile. Oh it had been one of the ones made on one of those free time .
I believe they are inclined to work on things early if it's very likely to pass a poll or whenever they may use the assets elsewhere. In this case it was directly according to a popular proposal from 6 months ago so they could guess it'd be well received. So they need to do a substantial amount of the work before bringing it to the survey.
I can not confirm whether it's true, but Jagex has been around record dozens of occasions saying they do not put significant dev time into pre-poll content. They mostly follow the suggestions and roadmap and get community input pre-poll. I am pretty sure group ironman was announced at runefest 2017 and was likely to be published 6 weeks down the street at the most recent. Idk why Jagex makes so many empty promises every Runefest; it is like they make all these programs and Buy RS gold when they get into the dev function they understand it is going to be a lot more work than they expected but they're afraid of being transparent with the neighborhood about it.