Unfortunately, there is a hint as to how this has happened:

"This strategy is no longer practical: users have come to rely on backreferences for at least occasional use, and backreferences are part of the POSIX standard for regular expressions."

What better excuse is there for a poor implementation than standards compliance? In many ways, using regex with backtracking by default is like programming in Lisp without tail-call optimizations. If the POSIX standard is going to require backreferences, then it should also require a non-backtracking implementation for regular expressions without backreferences, just like the Scheme specification requires implementations to support tail-call optimization.

The comparison is valid because they both can create a quadratic runtime from a linear time algorithm.