WARNING: The following contains spoilers for Digimon Adventure: 2020, Season 1, Episode 13, "Garudamon of the Crimson Wings," now streaming on Crunchyroll.
Digimon is named as such in order to give viewers some idea of what they might be in for from the get-go. The premise is right there in the name: Digital Monsters. So, understandably, you'd expect to see a few more Digimon like Lynxmon, the cat that's literally on fire, or Unimon the dark flying Unicorn, and the red Pikachu otherwise known as Elecmon. But no one would expect jeans to be such a monster trend in the Digital world. Just look at Leomon, WereGarurumon and Gargomon if you don't believe us.
Like the Pokémon Machamp's speedo or Jynx's dress, the preference for Digimon in clothing is generally unexplained as one of the "mysteries" of the show, and while some could chalk it up as just a design decision of the time (that time being the late '90s and early '00s), we beg to differ. We believe the jeans are somewhat symbolic of a very specific stage of growing up: rebellion.
Once you start looking into it, a few trends emerge. Firstly, most of the Digimon wearing jeans are at the Champion-level, but most lose them at Ulitmate or Mega. Secondly, while most human-like Digimon wear clothes, only a very specific personality type is associated with the jeans look. And finally, the more mature characters tend not to need them.
Jeans on a Digimon don't just symbolize rebellion in general; it's worth noting that they can symbolize a few different types of rebellion. There are a few of Digital denim-lovers that everybody knows, like the aforementioned Leomon and WereGarurumon, in addition to some lesser-known Digimon, like Yasyamon. And from these characters, an archetype begins to form of the noble freedom fighter, rebelling against a corrupt system, protecting the weak. Others, like SkullMeramon take things to the opposite extreme. Coated in the chains that for other Digimon are just accessories, SkullMeramon's skinny-jeans embody the tight restrictions that cause him to lash out in violent rebellion -- often eagerly attacking whenever possible.
Another possibility as to why so many Digimon wear jeans is because they're human-like Digimon, and there seems to be a relationship between "humanness" and the amount of clothing they wear -- ranging from Neemon of Digimon Frontier who simply wears a pair of oversized sweats, all the way to Laylamon of Digimon Fusion in her full-on evil ballgown. This also explains why so many jean-lovers are in the Champion stage, as that's when most Digimon start to take on human traits. On top of that, most of these jean-loving Digimon, true to their rebellious nature, refuse to fit into the human-not-human dichotomy and therefore, tend to be human enough to warrant some clothes, but need all of them.
Then, of course, you have the characters with nothing to hide. These Digital Monsters are completely secure in their identity and are ready to rumble or mentor, whichever the plot demands. Garudamon, who showed up in a recent episode of the reboot, looks at first glance like she should be wearing pants of some sort, but she isn't. She doesn't need to. Garudamon is calm, large and in charge, showcasing her maturity through her quick assessment of the situation and prompt action.
The jeans trend of the Digital World can clearly be interpreted as visual shorthand to indicate the wearers' key personality traits and desire to rebel. The fact that this usually happens in the Champion stage can be likened to teenage-dom, and while most abandon their rebellious urge as they "grow up" (Digivolve), some, like BanchoLeomon, never let go of their rebellious roots and keep seeking to make the world a better place. We hope they succeed.