The main difference between LGPL and MIT is that, in both, third-party programs that use the library can be non-free, but with the MIT license, modifications to the original library can be non-free as well. (LGPL requires that those modifications to the original library be relicensed under the LGPL as well).
Not sure what that translated to in the context of this project, but presumably they believe people want to be able to extend the library itself while keeping their modifications proprietary.
Comments
The main difference between LGPL and MIT is that, in both, third-party programs that use the library can be non-free, but with the MIT license, modifications to the original library can be non-free as well. (LGPL requires that those modifications to the original library be relicensed under the LGPL as well).
Not sure what that translated to in the context of this project, but presumably they believe people want to be able to extend the library itself while keeping their modifications proprietary.