You often hear the old trope that gravel is just an updated version of 90s XC mountain biking, so it's probably not a great surprise to see the resurgence of hydration packs, especially for those racing or looking to travel light by minimising the use of bags on their bikes.
There are many reasons to look at ditching your water bottles when riding off-road. Firstly, your liquid is well away from all the dirt and dust, so there's zero chance of grit in your teeth or for those in wet and muddy conditions and riding near agriculture, something potentially much worse. You can also often carry more liquid, with most gravel-oriented bags designed to carry around 1.5 to 2 litres of fluid. They also often feature extra storage, ideal for the essentials like multitools, pumps and tubes and food.
