No older person likes to be admonished by someone younger. Older siblings being corrected by younger siblings, Sons and fathers, Mothers and daughters. Even when the message is correct, to continue the onslaught just delays action, especially when the total answer lies beyond the powers of the person being chastised.
As we all know the World needs to come together to have any chance of stemming the tide of Climate Change. We already know that as a fact, but around the World there are 180+ odd different countries, some of whom are at war with one another, or with factions within themselves, they are killing one another right now... are these 'leaders' likely to listen to what might happen long after they are gone, whoever delivers the message?
Rich countries are the main polluters but whilst they may have lots of empathy, and 'celebs' and others make great play of being 'carbon neutral', the real sacrifices they have to make, seem unlikely to be achieved.
Emerging nations wanting to bolster their economies still need the carbon-based fuels as their main energy sources in order to achieve their aims of lifting people, hundreds of millions, out of abject poverty.
Poorer, usually smaller, nations are already getting 'stuffed' by the World around them and they can do little about that, let alone stemming Climate Change
Greta is of course delivering an 'inconvenient truth' as such, what ever her age, sex or religion she is the messenger carrying the message no one wants to hear and she is suffering the consequences, modern day Joan of Arc... maybe?