This chart is a huge oversimplification. The immigration process is complicated, confusing, and arbitrary.
I moved to the U.S. in the Fall of 2003 (nine and a half years ago!), to enroll as an undergraduate at Stanford University. I graduated in 2007, and have since worked as a software engineer at several high-profile tech companies. I was an instructor for a class at Stanford. I've spoken at many technical conferences and meetups. I've been asked to review technical books and have received inquiries from publishers about authoring technical books (but declined). I've created and contributed to many open source projects. I've never been convicted of a crime. I make a six figure salary. I pay my rent, my bills, and my taxes. Thankfully, I've been able to get student visas and work visas to allow me to do all this.
However, even after nine-and-a-half years of this, I am not a single day closer to having a permanent legal status in the U.S. than I was the day I arrived for college. In fact, if I applied for a green card today, I could get deported. and denied entry to the U.S. for the next ten years[1]. Why? Because my current visa status is a "non-immigrant visa", and showing "immigrant intent" (such as applying for a green card) would be a violation of my visa status.
I'm even in a long-term committed relationship with a U.S. citizen (4.5 years now), but disclosing this to an immigration official could also get me deported. Why? Because it's a same-sex relationship, which the federal government is forbidden from recognizing for immigration purposes by the Defense of Marriage Act (DOMA), so my partner cannot sponsor me for a green card. Yet the mere existence of such a long relationship could be construed by an immigration officer as "immigrant intent" and a violation of my visa status.
But I have a great, well-paying job with an employer that appreciates me and wishes for my continued stay in the country, surely I should be able to get an employer-sponsored green card? Well...
First, I would have to change my visa status, because my current visa status doesn't allow me to apply for a green card.
Second, the green card process is expensive. Tens of thousands of dollars in government fees and lawyers' fees. I would gladly pay the money (it's worth it), but that would be illegal. My employer has to pay. They can't deduct it from my wages, that would be illegal. They can't pay me a lower salary than my fair market salary, that would be illegal.
Third, the green card process is complicated. My employer has to post a job opening and advertise it widely. (Like, in newspapers. Yes, newspapers.) They would have to interview candidates to fill this opening who are U.S. citizens or permanent residents. They would have to find that all these candidates are unsuitable for the job opening. They would have to thoroughly document this process.
Fourth, the green card process takes a long time. Even after all this, there's a lot more waiting. As a Mexican national, software engineer, with a bachelor's degree from Stanford, assuming everything I described above went swimmingly and I've managed not to get deported, it would probably take me another ten years of waiting before being granted that green card.
Oh, and in the mean time... I can't quit my job. If I do, I get to start all over again. (When was the last time you spent 10 years at a single employer?) Every time I cross the border I'm treated like cattle (if I'm lucky) or a terrorist (if I'm not). Every time I renew a visa I'm treated like I'm trying to defraud the U.S. government. Every time I renew a visa I have to deal with the worst bureaucratic nightmare you've ever imagined. You can be given an appointment at a consulate for a specific time (9:10am), and yet have to wait outside in line for hours. I've waited in 120F heat. I've waited in rain. You're not allowed to bring cellphones, car keys, or even wallets into the consulate. (But how do I get home? They don't care. How do I let someone know to pick me up? They don't care. How long will it take? They don't know, and they don't care.) Each individual immigration or consular officer has total discretion to deal with my case. If that individual is having a bad day and doesn't like the look of me, they can deny me a visa or entry into the U.S. and make it basically impossible for me to ever get a visa or be allowed entry in the future. If that happened, I would have no ability to appeal to the U.S. judicial system. (There are separate "immigration courts" set up under the executive branch, where due process is laughable.)
And yet I'm among the lucky ones. I've been privileged to study at great schools, work in great companies, in a growing field that is in high demand. Most people don't get it this easy.
[1] Denied entry under _any_ visa. I couldn't work in the U.S., I couldn't study in the U.S., I couldn't visit family in the U.S., I couldn't vacation in the U.S., I couldn't even wait in a U.S. airport for an hour before getting on a connecting flight.