I see the trend in my coworkers at a big-four ad tech firm as well. At least a couple of them have gone home in the last six months (one of them had her H1B approved less than a year ago as well; and another one already is nearing her STEM OPT extension of 18 months).
I came to the US in mid 2000 to study at a fairly well-known liberal arts college (with full scholarships). I worked at a start-up in SF after graduating in late 2000--earning a decent wage of 72K/yr at that time. The CEO didn't want to go through the trouble of applying for H1B for me, so I--at the end of 18 months' OPT STEM extension; after ~2.5 years of working at that start-up---had to apply for a PhD program and started it in 2010's to keep myself in legal status. I finished my PhD in less than 5 years, and joined my current company with OPT (an extension of F1 student visa for practical training in one's major that s/he graduated from) earning low six-figure salary. When my company applied my H1B visa in 2016, it received request for evidence (the USCIS asked me to prove more that my work--data engineering--is related to computer science, which is what I studied my PhD on. I wrote up 3 pages of explanation and finally got it approved in late 2016. Because I worked pretty hard, I was able to convince my company to apply green card for me. But because of the more stringent regulations applied by Trump administration (and partly because my company acquired standard--not premium--service from the law firm that is working on my case), even after 2 years of the process, I am still at the very first step of the application process where the company is waiting for the department of labor (DoL) to provide prevailing wage determination (pretty much stating how much average worker with my salary is earning in the region where I work). I cannot move jobs when this process is pending because my H1B is tied to my employer and employers that are willing to sponsor employees green card aren't that plenty.
If I want to go back and visit my old and widowed mom in my home country, I would have to go through the interview process at the US embassy of my home country to get a new H1B stamp on my passport (the stamp expires within a year of issued date; some countries, such as India, have better deal with the US and their citizens usually get stamps valid for like 5 years or so if I remember correctly). It carries the risk that I might be denied either by the embassy or the port of entry immigration officer (none of the three that I have met so far treated me nicely--in fact, two of them were quite rude--despite me being courteous and nice to them) when I re-enter the US with H1B visa, not to mention that the cost of renewing the visa costs about $400. So, the ability to go back to home to revisit my mom as frequently as I like (without much hassle) AND the freedom to move to another job are why I really want to get permanent residency.
This is a common path for someone who goes through legal (hardcore) means to become a permanent resident in the US. I only put up with such extremely long journey to become a green card holder because my home country is not China. If it were China, I would be back there by now (I said the same to my departing coworkers). There are easier (in terms of effort/time required) ways like marrying a citizen; seeking asylum (but most of the asylum seekers are doing so for economic reason, meaning they are mostly fake although the success rate of getting approved in democrats administrations are quite high); winning Diversity Visa lottery; and having an immediate blood-relative who submitted application for your green card a decade ago. But none of them are eligible for me or I'm not interested in playing pretend-asylum seeker or paying a US citizen to marry me temporarily.
Throughout the years I've been in the US, I worked hard; paid all my taxes; never even have a minor violation such as traffic citation; donated and volunteered at various charities; donated blood more than a dozen times; etc. I thought I did pretty well as a good, law-abiding, immigrant-wannabe. During the ~16 years, I have experienced quite a few (at least a handful of times that I can recall--including being mocked with 'ching chong ling long' by a panhandler, who was trying to sell me a rap CD in metro area) obvious discriminatory abuse from random strangers (I live in a big metro area).
I am writing this in detail so that I hope HN readers would realize that it is not an easy route for many of the legal immigrants like myself. Sure some of the shady companies abuse H1B, but majority of H1B workers had to go through a pretty rough route to get their H1Bs. If you ask me, I would totally streamline the H1B system so that the companies are required to pay above the average salaries for H1B hires; H1B hires aren't tied to the employers; getting an H1B approved does not require law firms (quite expensive) and a lot of red tape (like in some countries, the wannabe H1B worker can apply for it her/himself); and more importantly, H1B holders (regardless of their country of origin) can enter and leave the US for either business or personal trips unlimited times without much restriction. Then I really do not have a need for green card because my goal is to eventually go back to my home country and retire there in my late 50s. Life in the US, in my opinion, is a lot more stressful than it should be for a developed nation (worrying about healthcare affordability tops the list for me).