The context here is that these people have publicly made the "Giving Pledge" to reduce their assets by half to improve society, and yet their assets have double

The context here is that these people have publicly made the "Giving Pledge" to reduce their assets by half to improve society, and yet their assets have doubled in a short time. That means they are underperforming based on their own intent, and casts doubt on the selfless virtue component of the Giving Pledge.