CBT is the main heavy testing, with the amount of content being added and removed during each test the testers HAVE to start from scratch. You can’t really use data from one CBT version if the next has skills or classes moved around in the game progression. For a hypothetical example, why would you have a C1 archer C3 QS if they decide to change QS and make it third circle instead of second?
CBT change so much content of the games between testing phases that it’s impractical for them to save the data to continue use. Also CBT is for testing issues and bugs with the game, not “playing” the game it’s the second of third testing states.
Alpha testing; where the game is tried over and over with producer tools to assist in making sure the game is in a playable state. Data is never saved between sessions as the people taking part can just ‘create’ the items and exp to test the content.
Closed Beta testing; where things are hunted down and tested in a larger environment because nobody is perfect and online games are so big that it’s very unlikely a small group would find most issues. Due to the nature of how drastic a game can change between CBT periods. See recently with how the game completely changed how you can pick a class when you advance a circle to include backtracking. 90% of the tests are with advanced EXP rates to get to the content being tested. Data can but rarely be saved between sessions.
Open Beta testing; the game is almost ready for release, Usually newbie area content and stress test. Most online games usually do not wipe after this stage any more, because at this point very little outside minor balance tweeks occur and fixing of game-breaking bugs that have slipped through. There is only one open beta stage, and it is almost always followed with release or cancellation.
Honestly if a game is good enough, you shouldn’t care about data being wiped until AFTER it’s released (A few games have had all their data wiped post-release but that is for a variety of different issues.)
International CBT have always been kinda shoddy and unneeded. All they need is an OBT to see if it works and the translation isn’t bugged and then go into release, IMC have been very generous letting other regions test the game this far from release.