How do anonymized datasets fall short of their goal of being anonymous?

Anonymized datasets aren't actually anonymous because many of the data fields can identify a user

Anonymized datasets can be traced back to the individuals by looking at their browsing history in the app

Anonymized datasets can be re$-$identifyed by anyone holding the hash key

Anonymized datasets can be combined with other datasets, which can re$-$identify individuals

What is a likely outcome for a weather app using a learning algorithm to figure out where to put their future weather stations?

Collecting weather data every time the app is opened, knowing the temperature where the app is being used

Collecting location data every time the app is opened, potentially learning where a user lives, works, etc.

Storing data in an AWS instance with all weather stations in the country

Accessing weather forecasts from local broadcasts