I disagree. Djokovic, with Rafa's attitude and team around him, would not have any problem being equally popular.
It has nothing to do with being Eastern European. When you come from a relatively smaller community or country (in terms of power), your controversies are less tolerated, unfortunately. It's a hard fact. When England and Australia dominated cricket financially, players from those countries could get away with many controversies. Players from India or South Africa didn't have that luxury.
Women are out, Croats are out, Jokic is out. We only have Djokovic in the circle now, so maybe it's not a systematic bias.
It is the "national" team, so they can exhibit some nationalism. As long as they don't sing and dance for a greater Croat nation, it's acceptable I guess.