Here's why:

* Conduction: While conduction does occur in liquids and gases, it's less efficient than convection. Conduction relies on direct contact between molecules, which is less frequent in fluids due to their greater spacing and movement.

* Convection: This involves the movement of the heated fluid itself. As a fluid heats up, its density decreases, causing it to rise. Cooler, denser fluid then sinks to take its place, creating a continuous cycle of movement and heat transfer. This is how hot air rises, creating drafts and making convection ovens work.

* Radiation: Radiation is the transfer of heat through electromagnetic waves and can occur in liquids and gases. However, it's less dominant than convection in most everyday scenarios.

In summary: While all three methods of heat transfer are possible, convection is the primary mode of heat transfer in liquids and gases.