This was one of those rules that the IAAF Technical Committee adopted to make it easier to read the photo. Several members of the Committee which included international photo finish judges said that in reality you only need a very thin black mark and everything beyond that is not necessary.
The sports governing bodies (IAAF & USATF) knows and approves that the timing companies will often enhance the finish line (never prior to the finish line) by extending black tape beyond the lane line. Omega routinely will place vertical pieces of black tape to assist.
This was part of an overall project to review all of the painted lines on the track. One other was the removal of the series of dashed lines (30 cm) prior to the finish line.
David Katz
IAAF Technical Committee
Editorial Board, member
IAAF Facilities Manual