On the question of “why do they collect all this data” - brightness, battery life, headphone usage, volume etc: It’s not just because the data is valuable in itself, it’s also to ‘fingerprint’ the device across IPFA boundaries and in the face of things like NAT and VPNs. There are so many disparate data points that are different across different devices that two apps reporting an identical or near-identical set in a short timeframe are likely on the same device.