The Porter stemming and Levenshtein edit-distance algorithms are not
"fast-moving" nor are they fusion reactors... they've been around
forever, and are simple to implement, but are still useful in various
common scenarios. I'd say this is similar to Python including an
implementation of digest functions such as SHA: it's useful enough, and
compute-intensive enough, to warrant a C implementation. Shipping C
extensions is not an option for everyone; it's especially a pain with
Windows.