Power Engineers: Why have DET replaced all the triangular phase poles that had fiberglass brackets?

Question

DET (Detroit Edison) did that in the year 2000 and I always have been wondering why they did that.

here's what the brackets look like:
http://www.epac.ca/products/insulators/specs/fiberglassinsulate.htm

Answer 1

I believe it was part of the huge overhaul in 1999/2000 which followed the investigation into Detroit Edison's (non-)compliance with the Electric Reliability Agreement which they had with the State of Michigan.
See work schedule A on http://efile.mpsc.cis.state.mi.us/efile/docs/12269/0005.pdf