What I really mean to say is that the people who show up to learn ukulele are almost always there to have a good time. Things are more complicated with the guitar-learners. Over the several years I've taught introductory guitar and ukulele classes for adults, often back-to-back, and I've noticed a few things.
The ukulele adoptees invariably have bought a colorful, delightful little instrument in a flashy soft case, or received one as a gift. They've already found a Youtube tutorial on the three chords to play the Lava Song. They have that gleeful vibe that expresses "I've joined a club of older adults quietly thumbing their noses at their uptight corporate jobs and saying yes to their joyful inner child".
The guitar learners, on the other hand, encapsulate a more varied set of emotions. Some have bought the cheapest guitar they could find on Amazon and found the strings painfully too high to press down. Many have downloaded a tuner app or found a clip-on tuner but have no intuition about which direction to turn the pegs to satisfy the blinking lights on the screen. Perhaps they've tried to fret a chord shape only to find buzzing or thunking strings and painful fingertips. Some folks on the guitar path have inherited an old classical guitar with corroded strings and noticed a gulf between the sounds coming from their instrument and the bright, aggressive strumming of their favorite Americana tune.
So why the vasty different experiences between the uke and guitar strummers? The physical challenges are clear--a steel-string guitar resists almost 200lbs of string tension and a ukulele, maybe 30. A setup is vital to a beginner's comfortable guitar-playing experience. The open strings on a uke already produce a lovely C6 chord, and the lower pitched guitar ring to the tune of open Em11. A C-chord on a uke is a one-finger-win. On a guitar, it first feels like the 'sit-and-reach' from gym class. The fundamental difference, however, I think is the emotional 'baggage-to-blank-slate' ratio, and it's simply not in the guitar's favor. What do I mean? Scroll through the years worth of world-class guitar players of every conceivable genre on Youtube--it's impossible, of course. However, since we are all primates and comparison junkies, it's difficult not to feel overwhelmed. Van Halen and Jennifer Batten, Kaki King and Andy Mckee, Tosin Abasi, Ed Sheeran...keep scrolling.
Now search for "ukulele cover". What do you find? I see someone smiling in almost every thumbnail. A much more even gender balance compared to the boys-club of rock & roll (notable exceptions of course). Kids in middle and high school playing pop tunes. Looks like inclusive fun, doesn't it? Guitar teachers, we've got some more work to do!