If the saving of “Auto recovery information” is enabled (menu Tools > options > load/save > general), LO saves each X minutes a copy of the modified file in your profile path:
You can open or copy this file to roll back the last unwanted, and still not auto saved, changes.
Attention: This backup file is deleted when you close the document in LO.
But your complain is right. It would not be a so big effort to implement the auto save, but this is the world of the Open Source software. Not only for LibreOffice. The developers receive donations from users but they set their own priorities. It is their right, but it is not the good way.
There is a plenty of annoying very old bugs still open after many years, and many small missing features, meanwhile the developers concentrate on a few advanced features, witch 95% of the users don’t use. It is not good for the diffusion of LO and other open source programs.