Q. Why does BE use new .bkf files, rather than overwriting old ones?
A. Go to Tools --> Options ---> Media Management and check that the following is set
If you set it to overwrite recycleable media, then it will not create any new .bkf files if there is a .bkf in the B2D folder that can be overwritten.
Setting this option to overwrite scratch media (1st option) can cause BE to create more and more .bkf until the disk is full.