To be fair Whatsapp works the same, if you are not careful when changing phone you will lose your history. That's because they don't actually store your messages on their servers, they are just synchronized between devices.
That's not the case though, at least for me? I had set Whatsapp to backup to Google Drive, and when I switched to an iPhone it did some automagix and all my stuff was there (and then backed up to iCloud!).
