I think the issue is at least partially a failure to present an alternative vision.

People do the things they do and consume the things they do in order to meet some need (stimulation, entertainment, pleasure, etc.). Although, I don't think it's unreasonable to advocate for some austerity, to a significant degree people are going to need alternatives that meet the needs that were formerly met by the things they are giving up.

It seems to me that environmentalists tend to fail to provide a vision for what those alternatives could be.

We may need to reconsider what is austerity also, is living without a pet austerity? is washing ourselves with a soap bar instead of a multitude of cosmetic products and stuff austerity? is eating local legumes/fruits austerity? is using a bike to commute or go shopping austerity? etc.. There are many environmental-friendly alternatives, I think it's every person's role to find those alternatives (politics are more interested to foster consumerism), this guy is quite inspirational https://www.youtube.com/watch?v=nX4kq4QfYRA