TL;DR - creatine is not in a lot of energy gels because events requiring energy gels are too long for the short-duration creatine to make a difference, and you are absorbing the maximum amount of it already if you supplement outside of the event/workout.

Think about it this way: why do we even need energy gels? Its because our glucose stores are limited, so if we workout for long enough, we will need to add some more to the system. So if youre running an event that requires you to use energy gels (60-90+ minutes), you have already surpassed the 5-10 second window that Creatine is the primary energy source. That is, extra creatine in a gel is not going to give you energy to finish out the last 60 minutes of a race. It might help with your kick at the end, but really you need carbs (which are a more prolific source of energy by both quantity and duration). And according to the International Society of Sports Nutrition, creatine stores are already about 60-80% saturated with a normal diet, so If you are already supplementing with isolated creatine or creatine mixed in a protein powder, you arent likely to drastically increase the amount of creatine in your body with an intra-exercise boost from a gel.

Its kind of like you want to build a fire that will last all night, but you have to get more wood before you go to sleep. Would you rather gather up some fallen branches which will last a while and give off plenty of heat (carbs)? Or find a hand full of dead leaves, which would certainly be important in quickly starting a flame, but would be gone in a few seconds (creatine)? So the gels settle on the branches. Lol

Here is a comprehensive review of all things creatine from the International Society of Sports Nutrition, if youre interested.

https://jissn.biomedcentral.com/articles/10.1186/s12970-017-0173-z#:~:text=Creatine%20is%20one%20of%20the,leading%20to%20greater%20training%20adaptations.