Because they usually grow in poor soil - specifically, Nitrogen poor soil. To simply live in that soil is impossible.
Thus, they need an external food source. By capturing and digesting insects (and other critters), they obtain the vital nitrogen they need to survive.
Most plants are lucky enough to just absorb the nitrate from the soil.
This pitcher plant is more than happy to digest this unfortunate mouse - beggars can’t be choosers.[1]
Footnotes
Ilgiardino.wiki
Because they usually grow in poor soil - specifically, Nitrogen poor soil. To simply live in that soil is impossible.
Thus, they need an external food source. By capturing and digesting insects (and other critters), they obtain the vital nitrogen they need to survive.
Most plants are lucky enough to just absorb the nitrate from the soil.
This pitcher plant is more than happy to digest this unfortunate mouse - beggars can’t be choosers.[1]
Footnotes
[1] The giant plants that eat meat