One of the best questions asked by a few people was "Why Andromeda? There's more than enough space/stars in the The Milky Way."
This is absolutely right, of course. There are trillions of stars in the Milky Way and potentially billions of life-bearing planets. More than the Federation could likely visit in its entire existence. Certainly more than any number of Star Trek series could depict.
But in all the various Star Trek series, we've already visited every quadrant and made the Galaxy feel small. I felt like it would be best to not pretend that' the mystery hasn't been lost from the Milky Way. Realism aside, Star Trek has made the Milky Way too familiar and boring through over-exposure. Humanoids with bumpy heads populate every single quadrant.
Now, at first, the idea of sending the Enterprise to another galaxy may seem like a lazy, reflexive choice. Unoriginal, even. But I put a good amount of thought into it and there are a lot of story and character related benefits to doing this.
The benefits you get from exploring a new galaxy are:
It's a catchier hook - a "high concept".
You can advertise/sell the show easier if you say:
"The Enterprise begins a new age of exploration in a brand new, unknown galaxy - Andromeda!"
than if you say:
"Starfleet explores a backwater of the Delta Quadrant that Voyager missed."
It's about the concept of frontierism and exploration, not strict realism.
Reflecting Today's World
You get to use the conceit of combining all the resources of a Galaxy (The Milky Way) on a grand endeavor - a mission of exploration and discovery. It forces disparate cultures to work together, through tensions and competing values and objectives. It reflects our modern world where we find ourselves intrinsically tied to other nations, economically interdependent. The US has to work with China and Russia; and the European Union struggles to hold itself together. This lets Trek be more reflective of the modern political climate.
This gives the show great potential for drama and intrigue that the modern audience can identify with. Like Russia invading the Ukraine - perhaps it's the Romulans taking back a Federation planet they say was theirs originally - are the Romulans returning to their aggressive ways? Would we turn on them and risk war, or negotiate? Or Greece's bankruptcy threatening the cohesion of the EU. What if Andorria was disastrously poor and the Tellerites, Ferengi and Vulcans didn't want to help them. Would the Federation crumble? Or the Arab Spring/rise of Islamic extremism. What if a Klingon revolution led to the fall of the Empire, then a violent Klingon cult tried to fill that vacuum and started taking over worlds, causing chaos in the galaxy?
Diversity and Mystery
You get a fresh start in a new Galaxy. You can get away from the budget-driven conceit of every alien having to be humanoid (so much so that they had to make the episode "The Chase" to explain how all the Humanoid species were related and seeded here).
Yet, because we still have all the old Milky Way species, we can continue to use them on the show, too. But they're not the aliens anymore, they're us, in all our wonderful variety. It makes our surrogates more diverse (reflecting our own modern diversity). One of the best decisions TNG made was to add Worf. To take a species that had been the "other", one-dimensional aggressive enemies, and make them "us". By making Worf a protagonist, we got to see the depth of the Klingon psyche and come to understand them. We came to see how they are really a part of us. The Klingons became the Vulcans of TNG. By letting us use all of the Milky Way species as "us" in Star Trek Beyond, it adds diversity to our own self-image (something I try to reflect in the makeup of the crew).
This also allows us to have true mystery in Andromeda. We can go back to the feeling of not knowing what to expect each episode when they arrive at a new planet. With the format of the series being more akin to a "Game of Thrones" or other premium cable series (10-13 higher budget episodes a season), the old limitations on imagination and science could be erased, allowing the aliens to be *truly* alien.
The Return of Frontierism
We get to see a real frontier story, more like TOS. In my series arc, the Enterprise is the first ship in Andromeda, but this is not Voyager. During the course of season 1, Starbase A-1 is being constructed, and by the end of the first season, 2 more ships will join the Enterprise (including one captained by a descendant of Kirk who feels like the Enterprise should have been her ship).
Choosing to explore Andromeda wasn't something I just did because it seemed more dramatic. I did it because I felt like it could take Trek in a new direction, let it grow, let it build off of what came before, and let it recapture some of its original "wagon train to the stars" spirit.