There are many factors why an eruv was not erected previously, but this is for another time. I did not say that they were not built properly, only that they are better today.
Why is this “for another time”? I would like to know. What is difficult in explaining why it took until after 2000 to properly build it. Were the doros that brought up mishpochos for the previous 40+ years in B.P. and Flatbush not entitled to benefit from an eiruv. If it were always possible, why was it not previously done?
Was Rav Moshe enabling these “askanim” with his psak or did he fall for their ruse?