I understand your point, but I don't think is 100% accurate. There are tons of tutorials on adobe.com and you can at least study some open source projects (such as Adobe core component) to understand how it works. If you mean there is no downloadable free version of AEM you are definitely right, but still some of the most important stuff can be learned by using the open source stack on which AEM is built, like Apache Felix, Apache OAK and Apache Sling. And I guess even in the current market if you have java skills and you know something about Felix, OAK and Sling it could be pretty easy to get a good job contract (maybe not at the same salary, but just with one year experience you can get a substantial increase).