Most modern "nicer" triathlon (not time trial, as it's not legal) bikes have integrated hydration and/or storage. Sometimes integrated in the frame, sometimes a removable front fairing, sometimes a bolt on fairing inside the triangle, sometimes a behind the seat tube faired storage box or hydration unit.
The fact that triathlons dictate that you must be self sufficient outside of stopping at aid stations for hydration/nutrition and you can't have a "team car" or would lose a crap ton of time stopping at a gas station or to stop and unpack your jersey or touring bag...........dictates the tech follows the need.
For road, pros have team cars and roadside feeds. They also use team tactics and the peloton to shield/rest. You can't draft in triathlon. For most recreational riding, there isn't a real need to be both super aero and ergonomic for on-bike feeding and maintenance. So bikes are made with the assumption you will attach separately what you need.
If you really want something more integrated........either ride a newer triathlon bike as-is OR convert one to a drop-bar setup. Some of the newer ones with disc brakes can take up to 30mm or even 32mm tires.