Are you asking why create more density around/within Portland?
Because rural and suburban sprawl destroys fragile ecosystems, habitats, leads to misguided "wildlife creep", and has a larger impact on global warming/carbon footprints. Building UP is always better than building OUT.
Maine also has an appetite for making Portland a LITTLE bit larger with more sustainable jobs rather than service-industry jobs that can often be volatile with economic headwinds. Better jobs will also mean more EQUITABLE wages for Mainers, who are severely underpaid. Maine also has an "age" problem. We have one of the oldest populations in the country with the majority of our youth leaving the state and never coming back. Creating opportunities here is what will keep talent, creativity, and families HERE.
Lastly, there is a massive housing shortage within Cumberland County, but not exclusively. We already know that suburban/rural sprawl is bad for the environment. These communities also don't have the infrastructure to sustain, support, or even consider the possibilities of adding housing. Infrastructure is not just water, sewer, electricity, roads - but teachers, police, EMS, fire, health care workers, and so on. Keeping the greater Portland area small only serves to keep it more exclusive, unaffordable, out of reach, and honestly less diverse. Communities thrive when they're diverse. Portland's renaissance is deeply owed to those who helped put it back on the map and made it interesting. And now those very people can't even afford to live here. Or even if they could, there's no housing for them anyway. Additional housing stock at least levels the playing field making the rental market more competitive. Currently landlords are charging more money simply because they CAN, not because they need to. Add the fact that we've had crap ordinances around Air BNB's sucking up housing.
So why make it more dense? Because it's better for everyone overall.
Want "pastoral"? Drive down Stroudwater toward Westbrook and see the cows along the last remaining farm lands. These farm lands can remain untouched if we capitalize on urban in-fill and having VISION. Something Portland has lacked for a long time (hence all the discussion about historic buildings). Redfern has done a great job with in-fill within the city. Portland has plenty of barren (yet somehow precious?) parking lots that have sat vacant for up to 50 years. That in itself is just WASTE. So let's add some housing, rather than let the rich white part-time Maine resident NIMBY's keep the area exclusive and unattainable. Let's add some culture, vibrancy, fresh blood, and sustainable jobs.