The difference here is more likely to be between the Kindle (a notably low-power-draw device) and the other newer devices, especially the ones whose charging ci

The difference here is more likely to be between the Kindle (a notably low-power-draw device) and the other newer devices, especially the ones whose charging circuits are designed to take advantage of modern USB-C power delivery capabilities because people want their devices to charge faster. There is nothing inherent to MicroUSB that draws less power except that it is older than the standards that allow USB to provide more power (and thus used in devices that don't draw as much power).