I dunno.
I'd chalk it up to some of the same evolution in FF gear over the last several years toward longer rods and more of a Euro style in equipment that seeks greater reach. Many sling packs now are designed so as to allow for the placing of a long handled net through the sling harness.
It may also be linked a bit to something of a "guide fashion" that is more prevalent now in FF media - guides, especially those who own drift boats, have used long handled nets for practical reasons and this may have made an impression too.
While I'll concede that the larger, longer handled nets commonly seen these days have their advantages (just as the longer rods do) I can't help but shake my head when I see guys chasing gemmies and busting brush on tiny streams with a huge rubber net with 2' handle stuffed down their back. :roll: