Question

why some oviparous animals living on land lay lesser eggs as compared to living in water

Answer 1

oviparous animal are not living in water

Answer 2

oviparous land which live on land are able to find the safest places to lay eggs. they can also guard them till they hatch. as the probability of survival is more, the eggs are less (more eggs will mean more offsprings which will lead to overload for parents, death of offsprings due to hunger and cannibalism).
oviparou animals which live in water cannot lay eggs in water. they come to land to lay eggs . but they cannot guard eggs . the eggs become easy prey to other animals. thus to increase the survival rate, the eggs are more in number.