Why is it advisable not to dive after flying?

The most suitable reason for avoiding diving immediately after flying is the increased risk of decompression sickness. When you fly, you are exposed to lower atmospheric pressure than what you're typically under while diving. This can lead to nitrogen being absorbed into the body's tissues at a higher rate. Upon descending into the water, the pressure becomes greater, which affects the dissolved nitrogen in your body. If you have absorbed a significant amount of nitrogen during a flight, and then you dive, the rapid change in pressure can cause this nitrogen to come out of solution and form bubbles, leading to decompression sickness. Therefore, allowing adequate time between flying and diving helps mitigate this risk, ensuring that nitrogen levels have reduced sufficiently before engaging in diving activities.

The other choices do not accurately address the primary concern associated with flying and diving. For example, while we must always be mindful of oxygen absorption, that is not a direct reason related to the decompression concerns in the context of this question.