If you consider all ukuleles sold every year, tenors are probably not more popular than concerts and sopranos. If you look at only specialized vendors like HMS, they probably are the most popular size.
I think there are a number of reasons for that, all of them speculation on my part:
- We live in a "bigger is better" society. Doesn't matter if it's TVs, mobile phones (surprisingly), and cars, there is somehow that belief that if it's bigger, and especially more expensive, it's also better. Tenors are both bigger and typically more expensive (comparable quality given).
- Bigger ukuleles sound more like guitars, and we have been extensively exposed to that sort of sound since at least the fifties, and since habit and exposures often create preference, we experience the more guitar-like sound. I've noticed that some, perhaps many, tenor players eventually seem to drift to bigger sizes still, like baritones and eventually small guitars. Can't be generalized and it's just an observation that may well be impacted by my bias.
- Unlike in previous golden ages of the ukulele, high profile individuals (celebrities, media stars) play tenors, and if the pros use it, it got to be the "best" -- or so may be the perception. Most of today's big names play tenors, and they typically play them like small guitars.
- This forum is not representative of the entire ukulele community. If I had access to only $100 and wanted to just play music for myself, learning some simple tunes, this forum would not strike me as a good place to hang out at, because I'd feel out of place. Most of the people that stick around are hardcore fans of the instrument, many collectors among them, and generally a population that is crazy about the instrument that far exceeds the average, myself included. So we typically have five or ten or more instruments, and part of the journey is to explore all the sizes. We also spend increasingly more on our instruments (until some of us bounce back and realize that less is more). In short, this forum does give a bit of a skewed impression of what the "real ukulele world" may be like. The European forums also seem to favor sopranos (I found that interesting).
- And finally, and I feel most importantly, there is the element of vendors fostering and promoting tenors. There is a HMS video where Aaron essentially and literally says that sopranos are for beginners and children, concerts are often chosen by women, and men go for tenors -- then he makes a cooing and mhmm-ahhhh noise as he pets his tenor. This creates the perception that tenors are for real men, the real thing, the ultimate ukulele. Many other vendors echo the very same thing in the "which size should I choose?" sections on their shop pages, often saying things like "tenors are the choice of the serious player" or "tenors are the pick of the professionals". Whether that is deliberate, because tenors typically cost more and may well have a higher profit margin, or it's just their genuine view, or whether they repeat what they saw elsewhere, or a bit of all of these, it's all over the place.
And it makes you feel like you're missing out if you play a "lesser ukulele". You know, one that is for children and women.