Its a beautiful open source effort but products that have bugs like that languish for 10-20 years just aren't reliable. I need my mail client to be reliable.
But we should not spread FUD. If you can link to the bug I'd be interested, otherwise it doesn't add much value to claim this.
* there are rare cases of a profile either misplaced (exists but not correctly pointed to) or gone - it is something which I understand Firefox people are working on (Thunderbird uses the Firefox profile system) * there are extremely rare reports where prefs.js is corrupted * there are no compact failures in current versions - there are no open bug reports for recent versions, so it has been totally obliterated by a rewrite and subsequent fixes. Most user reports of compact failure are attributed to other causes of folder corruption * folder corruption can occur as easily from external sources as from product bugs.
Anyone who has a problem can file a support request at https://support.mozilla.org/en-US/questions/new/thunderbird to get assistance.
Also, beware drawing broad conclusions about other users' experience from one's own personal experience. I have almost never experienced corruption - once in the last 10 years. But I am also using a Thunderbird profile that has gone through 5 different laptops, two different OS, using daily builds, which is AMPLE opportunity to have had multiple catastrophic failures. But because I know other users experiences I consider myself lucky.