At bare minimum its to show that there are still groups willing to oppose mass polluters in the hopes that at some point someone with power will make the right call and save the planet.
Is it naive? Quite a bit, but sad complacency isn’t helping much either. As many of these groups are quite young many including Greta may also go into actual politics later in life, then these past incidents serve as proof of authenticity, similar to the pic of Bernie Sanders getting carried away.