The original statement referred to by this question is:
The more I ponder the principles of language design, and the techniques which put them into practice, the more is my amazement and admiration of ALGOL 60. Here is a language so far ahead of its time, that it was not only an improvement on its predecessors, but also on nearly all its successors.
(From the appendix of a very readable report on programming language design by C. A. R. Hoare. I read that report because I wanted to ask this question, not the other way round. Reading that report made it clear to me that the original statement is even more true than I thought when I decided to ask this question.)
The intention of this question is to better understand the sociological and political aspects of the events, not the detailed technical merits. The politically accepted successors of Algol 60 (at the time) like Algol 68, PL/I or Ada were badly feature bloated, while really improved successors like Algol W or Simula were never widely used. The surviving members of the Algol language family seem to prefer naming Pascal as their great-grandfather instead of Algol, even so Pascal seems to be just another descendant of Algol. (C or Smalltalk are not descendants of Algol, because their syntax and underlying principles are too different. C++ on the other hand might be considered as a legitimate descendant of Simula, embodying many of the same underlying principles, adopting the C syntax and legacy only for political reasons to avoid the fate of the Algol like languages.)
An account of the history of types in programming languages made me realize that even the type system of Algol 60 was still quite unfinished. It seems that it would have been easy to just finish the type system and fix some other minor annoying details for the next revision of the language. But instead... ??? Most of my math books use Algol for their pseudocode, and it looks much nicer than the C pseudocode in the few books that don't use Algol. So I always wondered why Algol actually died.