We are not doing anything to protect the cache. Android fully manages it. So, I don't really know why it doesn't clear it. It has been like that since day 1.

However, 1GB of cache is actually super easy to reach with just profile pictures. Many of the animated pictures are 20-50MB in size. You only need 20 profile pictures to reach 1GB. Sum all the uncompressed videos/pictures people send and boom GBs of data.