I understand the argument you're making. From the perspective of the United States, they don't need to care unless it adversely affects the United States. As such, the US can make whatever immigration it wants and it writes its own destiny and people can take it or leave it much like many offerings we see in life from companies, other people, etc. If a company is putting onerous conditions on its product, we'll switch. If a government is being a jerk about immigration, they'll lose out on great people.
However, I think a difference is that with a product or service, we generally all start from the same place. One day you don't have a cell phone, then you evaluate different services and choose one. Great. With citizenship, most are born with one. I'm lucky enough to be born with three and entitled to a fourth. Am I a better person than you? Why should I get out of this nonsense? (I know this isn't a great metaphor, but hopefully it makes some sense).
Now, these states have determined that I'm a member. However, I didn't really do much to merit membership. I just lucked into it. Basically, on this planet, I have more rights than most people - and that doesn't seem right to me. If I want T-Mobile service, I generally have the same rights as everyone else. Maybe there are discounts for people with certain employers, but it's more equal than unequal. With citizenship, I get a step ahead. While one can argue the merits of citizenship, I think a bit of respect in the process is warranted given that millions are allowed in by no merit of their own.
In this case, US policy is denying someone respect/dignity in accessing something they want: a job, a location, etc. Ok, so you can avoid that by giving something up (the job, location, etc.). What if the US decided that your state was "harbouring terrorists"? Well, you could give up that place as well and avoid the perils of living in a place being invaded/liberated. There is a slight distinction between something you already have and something you want to gain, but when you have a green card, it's kind of something you already have.
I guess my point is that libertarian ideals work great when there's lots of competition, a lack of strong power dynamics, and clear metrics. Here we see a situation with minimal competition (few "elite" economies), a clear disparity in the balance of power, and the cause and effect between treatment of individuals like you and macroeconomic policy is murky at best.
In this case, I think it's fair to call out the problem. Maybe American people don't know that they're losing out on awesome people like you. They should know that. People should know that you would be a great person to have and that US policy is making it so that you won't even consider the US. People (including leaders) can be oblivious to problems. Shining a light on problems like this can lead to change.
From a pragmatic point of view, there's the world-as-it-is and we need to choose between our options as you did. However, I think it's also important to try making things better. Should we not complain when Gmail makes a change we dislike? Google doesn't owe us anything and there are alternatives, but we care about it and want it to be better. We care about Google. We care about our friends who also use the service. Google is important and so it's natural to care about it and for Google to be the best it can be. Similarly, many of us care about the US. It's important; its policies affect hundreds of millions around the world (if not billions); many of us are American or are friends with Americans. I think it's natural to want the US to be better. It's nice when things can just take care of themselves, but sometimes that isn't the case.