Here's why:

* Fungi are heterotrophs: This means they cannot make their own food like plants do through photosynthesis.

* They lack mouths and stomachs: Unlike animals, fungi don't have digestive systems to break down food.

* They secrete enzymes: Fungi release enzymes outside their bodies onto the food source. These enzymes break down complex organic molecules into simpler substances that the fungi can absorb.

* Absorption through hyphae: Fungi have a network of thread-like structures called hyphae. These hyphae have a large surface area that allows for efficient absorption of the digested nutrients.

So, to sum it up, fungi obtain nutrients by secreting enzymes to break down food and then absorbing the digested nutrients through their hyphae.