Long waterline hulls go faster because they handle the bow wave and other elements of hydrodynamic flow better. That also gives a second benefit. MORE GLIDE. More distance per stroke. Everybody from kids to old folks wants to go farther with less work.
The one thing that stays the same is an individual's ability to generate horsepower over a long period. What's left to play with is reduced weight and waterline length.

: I have built two S&G kayaks by Eric Shade, the Widgeon, that are 14 ft long
: and 24" wide. I am contemplating on building a narrower strip kayak
: for learning to roll. I am 5'8" and 140Lb. Why do most people choose
: such long (17-18ft) kayaks? I understand the advantages of higher hull
: speeds and higher volumes to carry gears, but don't plan on doing any
: racing or over-night camping, just paddling in local lakes and Long Island
: Sound on calmer days. I had drawn up a few 14x20 kayaks with Ross Leidy's
: Kayakfoundry, with design displacements of around 185Lb with 3.5"
: draft. Before I cut wood, any suggestions or advice?

: Thanks, from Guilford, CT.