Mockito focuses on having a very simple and clean API to allow ease of use and a simple way to get started. It allows users to use the same techniques when mocking classes or interfaces as there is only one kind of mock and one way of creating mocks.
Users can easily track failed verifications in tests and these exceptions lead the user to the actual point of interaction in the code. The stack trace will always be clean and verification can be flexible in the order it is presented ensuring the most important verifications can be shown first.
Although Mockito is a mature framework it lacks the ability to mock static or private methods. This is because Mockito prefers object orientation and dependency injection over static, procedural code that is hard to understand & change.
The official tutorial contains thorough explanations and discussions of all methods, annotations, fields etc.., with lots of easy to understand examples. The API documentation is very complete as well and it provides detailed explanation for all elements of the mocking API.
Being able to capture instances and mock implementations as the test executes without having any knowledge of the actual implementation classes allows JMockit to verify these special objects through regular assertions with custom validation methods for each matching object.
Although EasyMock has great resources including their User guide and Javadocs, there is a need for a dedicated community that it seems to not have. Other frameworks have more support and community around them resulting in more developers choosing other frameworks.