For stuff that's neat. Neat article? Neat video? Neat pic of a bug you saw? All good. Neat meme? Ehhh... take it to the meme subs.
I didn't read this, but it's probably because plants aren't eating animals for calories, only for trace nutrients, and they don't need very much of those
If they could get more nutrients, that would put pressure to focus on the nutrients from trapped food compared to sunlight/environmental sources. They currently get enough from the insects to develop traits to get what they do while other plants don't.
I figure it is a structural and/or digestive limitation. Small bugs are comparable weak enough to be slowly trapped or drowned without being able to do enough damage to outpaced the effort on the plant's part. As bugs as plants and bugs scale up their mass in strength are exponential to their length and height so it would be harder to trap them and it would take more energy to create whatever they use to digest. If it wad even slightly better on the return overall, they would scale up until they reached the limit of that benefit.
Gonna go read the article as see if that speculation was right.
Edit: we were both on the right track. They do only need the trace nutrients and evolving the things to trap larger isn't worth the effort, but the main reason is that plants get plenty of nutrients normally and only evolve the ability to trap to cover for deficiencies in the environment in the first place and one plant drops that ability once it grows large enough to get energy an nutrients the regular plant way.
The world doesn't think like a corporate strategist...
Carnivorous plants trap prey because they live in nutrient deficient substrates. The primary nutrient in low supply is nitrogen. Nitrogen is a limiting factor on growth size. So one reason for their small size is that eeking out nitrogen from prey is a slow process and provides only so much.
Another reason from the article, trapping larger prey would require more complicated traps, which would require more nitrogen.
“Carnivorous plants already grow in nutrient-poor habitats,” Sadowski says. The plants have evolved their various trapping mechanisms to feed upon animals because they are unable to get all they need from the environments they grow in. Carnivory is a workaround to be able to grow where they are. The biomechanics of a trapping mechanism strong enough to hold bigger animals aside, a larger carnivorous plant would have to grow in a habitat with better soil to get so big, in which case there wouldn’t be much reason for them to be carnivorous at all.