It's difficult for me to agree with the notion that the offshoots of minimalism are not minimalist but maximalist. The ideas that the minimalists started with were simple enough but Reich and Glass expanded their approach into larger canvases. When Reich has, over the years, made cases that his compositional approach has seeds ranging from Handel and Bach (first prelude of the WTC, anyone) along through aspects of Beethoven's Grosse Fugue up into what he's known for that shows that Reich's conception of his music is not strictly to minimalism because it shouldn't be construed as any purist notion of a musical style. "The Desert Music" could be considered maximalist on the basis of instrumentation and scoring issues alone. Music for 18 Musicians sounds massive (and it is massive in case anyone somehow doubts this, which I doubt).
The pun is unavoidable but if we consider minimalism in light of a minimal definition it can be construed as a response to the entrenchment of total serialism and atonality. It wasn't necessary for minimalism to stay strictly in the serious concert halls. If anything the suffusion of the minimalist sound back into popular music ranging from industrial/trance/techno into New Wave and parts of "art rock" suggests how important minimalism has been. A band like U2, for instance, owes a great deal to the minimalists whether or not Bono and company necessarily tip their hats to Riley, Young, Glass, and Reich. If anything pop music's minimalism is consistent with the originally artier conception for sticking to more or less modal or tonal contours and going with simple musical forms. Making a case that minimalism has somehow stopped being minimalism because of pop music assimilation or a "maximalist" application of "minimalist" concepts comes off as the kind of strait-jacketing definition of concepts against which, arguably, minimalism developed as a correction.