Wrox tried that and it cost them their heads. Due to the extremely short timelines involved the quality of books went down, people lost their trust in the brand and stopped even buying the solid books Wrox also put out, and the entire house came tumbling down.

With fads lasting a few months at most the time is too short to write a book about them which hits the market up to date on the product when it is released and then gain enough sales to turn a profit before the fad ends.
Wrox countered that with their "beta books", books covering beta (or even alpha) versions of products and technologies in the hope those could then be updated to become the final book covering the final release version.
This approach has several problems:
Many such techs change considerably during that stage, causing largescale rewrites.
Customers feel cheated when their book about the beta product bears no resemblence to the final product.
And many customers probably expect some sort of upgrade path from the beta book to the (maybe never to be released) final version, something not offered.

Your comparison to fashion is valid in so far as magazines indeed can (and already do) pick up every latest fad and blow it way out of proportion as the best thing since sliced bread.
I doubt fashion books do the same. I'd venture that most will talk about more fundamental things like the best way to stitch a seam so it doesn't come loose rather than whether a skirt should be up to just below or just above the knee.