It basically comes down to dealerships, warranty and customer service in your area more than anything else. These days there is very little difference between brand bikes at the same price point. Apart from available colors it's just slightly different frame shapes and geometry, and even those differences are mostly minuscule. And no matter what the decal is on the frame, it's more than likely produced in one of the handful big factories in Taiwan that make frames for everyone (or China for the more budget end). Parts like drivetrain, brakes, suspension etc. are provided by 2-3 big companies and tend to be the same on different brand bikes at the same price point, with a few exceptions, where some brands are sometimes able to offer slightly more value either by selling directly to customer (e.g. Canyon) or by economies of scale (e.g. Giant).

There are some nuances like proprietary design parts on some bikes, but that's the general picture.