Jessie and James are as much of a staple to the Pokémon anime as Ash and Pikachu. Ash has traversed many regions, meeting and parting ways with friends and Pokémon alike. However, the one dynamic that has never changed is Team Rocket's pursuit of Pikachu.
After more than 20 years of trying to steal a single Pokémon, what if the mischievous duo decided to quit the criminal organization and go on a training journey of their own instead?
Team Rocket are not very skilled battlers, as evidenced by how frequently they're sent hurtling into the sky by children opponents. Yet to their credit, the crafty criminals do love their Pokémon. Forming a bond with one's Pokémon is the first step to becoming a legitimate trainer. Several of James' Pokémon in particular have had a habit of turning back to hug him when released from their Poké Ball.
Jessie has entered several Pokémon Contests over the years, though has never won, and even wanted to be a Pokémon Nurse when she was a child. Sadly, she and James received the lowest scores in the history of the Pokémon Training School they attended as kids, so a love for Pokémon doesn't necessarily translate to important training skills. This failure during their formative years was likely a major factor in their decision to join Team Rocket.
If nothing else, Jessie and James are persistent. After all, they've been trying to steal the same Pikachu for over two decades now. While they never give up, they clearly don't learn from their mistakes either. Adapting to overcome adversity is a crucial aspect of being a Pokémon Trainer. The Team Rocket misfits have been using the same tired schemes to try to steal Pikachu over the entire series.
The pair do form bonds with the Pokémon they catch, but they never keep more than a couple with them at any given time. And with the way they seem to neglect training their Pokémon, any gym leader would wipe the floor with them. As a result, they would more likely try to cheat their way through the gym challenge rather than strive to be stronger like Ash.
A major detriment to the possibility of Jessie and James going on a Pokémon journey is that they have jobs, and are technically at work whenever they're trying to steal Pikachu. In fact, the entire reason they've set their sights on Ash's Pikachu is that they want to impress their boss, Giovanni, who doesn't come off as the type to allow his Team Rocket employees to take vacations.
Extreme codependency also appears to be a struggle for the literal partners in crime. Jessie and James don't really form personal connections with anyone other than each other. They have an antagonistic relationship with everyone else they interact with on a recurring basis, whether it's Ash's group or their Team Rocket rivals Butch and Cassidy. Even their interactions with Meowth are mostly filled with personal jabs and negativity.
Their relationship with Ash, however, is a strange one. On multiple occasions, they've openly rooted for him during his matches. Sometimes they simply dislike the person he's battling, or they have sympathy for one of his Pokémon. Jessie and James have been all over the map, alternating between the young hero's enemies, simple nuisances, and sometimes even his allies. This wishy-washy behavior may imply that the villainous duo is unsure of who they actually want to be.
Put simply, Jessie and James are not mature enough to go on a Pokémon journey. Unable to outsmart or overpower an unsupervised 10-year-old, their tenure on the long-running series has been one failure after another. The longtime teammates must find a way to grow as individuals first. They can only endure so many electrocutions and high-altitude free falls before it's time to reevaluate their life choices.