Welcome to CodeRanch, Marco!
There are many ways to compose enterprise applications' business layer. Early EJB version were bit of hard to use since there were many unnecessary (compared to other lightweight frameworks came lately) work/development to be done by the developer. Most recently there have been a huge improvements to the specs similar to that of the lightweight (web/business) frameworks provide.
EJBs are primarily focused on the business layer (and the persistence layer with the JPA support) of an application. There are many other frameworks which can be used to achieve similar results. But it can be a preference of a given project/company to use certain technology provider for their application. And most importantly the ease of use (as EJBs becoming more lightweight and easy to use over time) is a key factor.
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