Why do you think Russia has such a pro-arabic politics?

It could be because Russia has a large proportion of its population which is Muslim, and consequently takes that into account in foreign policy, just like Franceor to a lesser extend Germany do.

Also, the Arab world is at loggerhead with the West, and Russia has seized that opportunity to befriend Arab nations. following in the example of the Soviet Union which was a champion of Arab nationalism and helped Egypt, Syria and Libya.