Why might a lizard need to sun itself, while a shark does not?

Question

a land-dwelling creature vs. a water-dwelling creature..

Answer 1

reptiles regulate by their body temperatures behaviour, such as basking in the sun or moving between warm and cold spots.

Most sharks are ectothermic (cold-blooded). Their inner body temperature matches the temperature of the water. However, some sharks, like the great white, can elevate their body temperature above that of their surroundings.

Fish change depths in the water column to find a suitable temperature, so probably sharks would do the same i assume.

so sharks would just use depth to regulate temperature.  

Answer 2

The lizard lives in an environment where temperature changes pretty significantly between day and night, and must warm itself each day after cooling off at night.

The shark lives in an environment with near-steady temperatures, or at least it will choose its depth to maintain a temperature that it prefers.