Earth, the colonies, the poor
Going back to ME1, it's just… very clear that the outlook for a lot of people on Earth in the 2180s is… horrific.
Basically, every colonist we meet is eager to escape Earth. This is especially obvious with the people of Zhu's Hope on Feros, or in the cut content for Caleston. If we piece everything together, when you want to leave Earth and have no capital or marketable skills :
you can join the Alliance military and benefit from the Deferred Education Plan (if you don't die in the line of duty first !)
you can, apparently, go to some bureaucratic entity called Colonial Affairs, which sets you up for a colony and definitely isn't downplaying how awful and dangerous it gets because they want as many colonies as fast and far as possible (Fai Dan : "Life is hard and often brutal, even without our current problems. Colonial Affairs back on Earth told us we'd be beneath the notice of any raiders — I guess they weren't counting on the geth." Hollis Blake : "It's a little different from what they claimed."), and worst of all it pushes you toward "corporate sponsors" like ExoGeni or Genex Chemical who are eager to make a profit on your back and at your expense (presumably to offload the financial burden of setting up colonies to the private sector ?) — and if I take Arcelia at her word when she says that "most of us" worked for ExoGeni, that means the colonists are also contractors, liable for damages if they do not fulfill their end of the bargain.
you can bypass the Alliance's bureaucracy entirely and go straight to Eldfell-Ashland Energy, who'll give you a job and an education through their subsidiaries, though you'll eke out your contract in a company town for God knows how many years.
per cut content, you can also benefit from an aid program called "contractual transit" (basically, an organization pays for your transit off-Earth to a location where you'll get to work) except when you end up on an independent colony technically outside of the Alliance's jurisdiction you've got no protections and might end up becoming a debt slave who's ruthlessly exploited.
if you can somehow scrounge up enough resources, you can set up your own independent colony outside of the Alliance's purview, like Horizon… but you're entirely at the mercy of space bogeys. And with no prospects. So the best shot for your kids, like Traynor, is… the Systems Alliance military, and the Deferred Education Plan.
"Colony Life — It's Not That Bad !"
Also, here's a completely accidental possible explanation as to why Americanish people are overly represented in the Alliance : per the first book, at least some parts of the UNAS (e.g. the Texan megalopolis) are among the poorest on Earth, period. So, uh, I guess people might wanna leave ?