Eclipse guidelines distinguish between two types of interfaces provided to third-party developers, i.e., APIs and non-APIs. APIs are stable and supported, while non-APIs are unstable, unsupported and discouraged as they are subject to arbitrary change or removal without notice. In our previous work, we found that despite the discouragement of Eclipse, the use of non-APIs in Eclipse third-party plug-ins (ETPs) is not uncommon. Furthermore, we found that these non-APIs are the main cause of ETP incompatibilities in forthcoming releases of the Eclipse. In the current work we conducted a survey aiming at understanding why do the ETP developers use non-APIs. We have observed that developers with a level of education of up to master degree have a...