Could you help me understand that prevents the use echo cancellation in FS

On the one hand SpanDSP library compiled with FS and contains functions for echo canceler libs/spandsp/src/echo.c

On the other hand FS does not contain applications of echo canceler. Also, I found the discussion in which states GPL is not compatible with the MPL1.1 and it prevent use Oslec (SpanDSP is uses Oslec).

Sergey