Because the black hole can't form from a star of 50 to 130 solar masses but it can, for example, start at 40 solar masses, collapse into a black hole, and then

Because the black hole can't form from a star of 50 to 130 solar masses but it can, for example, start at 40 solar masses, collapse into a black hole, and then accumulate another 20 solar masses over its lifetime to become a black hole of 60 solar masses. Edit: the mechanics of this are left as an exercise to the reader.