Experts might in a position to give a satisfactory reason. If they are really doing so, it seems good to me. Their research works are likely to be circulated among more people.

Basically, this is not peculiar to Arabic researchers. Considering the universal use of English as the "lingua franca" (of science) for academic purposes, it is not so hard to guess the reasons of the tendency of English among Arabic researchers. To me, this could result mainly from such occasions as: (a) to broaden the target scientific audience, (b) to share their research across a number of disciplines, (c) to disseminate research findings widely rather than in local contexts, (d) to publish research papers in distinguished international journals, and so forth. On the other hand, it might be solely due to the English-medium policies adopted by mainstream academic publications.

I think it is for linguistic imperialism that motivates all of us to learn English.They (The Arab) feels empowered to use this than their native language.

I totally agree with the reasons mentioned by Hulya Avci, I also want to add that not all Arab researchers are keen to write &publish in English, only researchers who specialize in pure or applied sciences, while most researchers on arts and humanities write in their mother language, this is logical because most of the knowledge sources in science and technology are in English, for example, if your research area is software engineering or cloud computing... It's hard to find valuable resources in languages other than English, so consequently, it become easier for you to write and publish in English... rather than in your native language.

Regards