Not all PurpleAir sensor owners opt-in to send sensor data to WU, so you will find many PurpleAir sensors missing from the Wunderground map.
In addition, WU seems to only use the air quality data from our sensors on their map. This may be because they support other weather stations that produce that data and due to the fact that the temperature readings in our sensors are meant for the sensors themselves. More information about this can be found here: PurpleAir Sensors Functional Overview
We’re open to your feedback about how to make our map more user-friendly. In the meantime, you might consider using one of the many third-party apps created by our users. A few of them can be found here: Q. Does PurpleAir have an app?