I can't speak to why the reasons to structure base game the way it was structured were made - they were before my time.
As for the quoted bit, this is the million dollar question, right? Though, for one, the player character can't be virtually anyone - we can't support that. The player of PoE and Deadfire always takes on the role of the Watcher. That character can be a lot of different things, but they are ultimately always a Watcher, they always have arrived in the Dyrwood from a foreign land, and they always claim Caed Nua, to name a few things.
(It's worth noting that I put limitations on tabletop characters, too. (And my guess is that most DMs do, whether it's in the races the characters can be from, the classes they can take, or where they can come from in the world.) My most successful tabletop games have had pretty tight restrictions on character creation. A Mage game that I ran for five years required all of the players be college students who were friends at the same school in Chicago, for example. Providing that tight guidance helps the player understand the type of game they're getting into and the kinds of challenges they can expect to experience.)
So the question is, how do you make that character's journey and goals as compelling as possible to as many people as possible? (Because pleasing everyone is somewhere between incredibly difficult and impossible.) I'd argue that you should present goals that are specific enough to inspire investment while universal enough to apply to as many people as possible. That's why hooking things on family can be problematic - the quest to save your child may not resonate strongly with people who don't have children or don't want them.
It may actually be more important to avoid alienating people than to net as many as possible. Generally players come to the table wanting to play.
And ultimately mileage varies. I love New Vegas, but the initial critical path (find Benny) didn't really grip me. I was just excited to explore and learn about the characters. But by the time that game's ultimate showdown came around, I was invested in the region itself, and the communities I'd impacted along the way.
I do think that it's also worthwhile to provide multiple motivations. Give the player several reasons to want to do something, and you're more likely to hook them than if you only provide one.
It wouldn't surprise me if new portraits crop up down the road, but I'm not the person to ask. I do think that there are a lot of options for portraits out there in the world, from fan-made portrait packs to commissions.
I don't think, however, that the goal of the concept artists (and I'm not one, so take this with a big old saltlick of salt) is to reflect only those traits available in the character creator.