It was the only language available at the time suitable for embedding. Memory-safe, small interpreter, sane. Alternatives were Forth and TRAC, which would have been much worse. Pascal would have been better, but it was too hard to squeeze in. The program and data had to fit in 640K. The program was built as a tree of overlays and code was swapped in, so less used code wasn't resident. But it was a cram job.

(I did some AutoCAD ports and drivers.)