The avocado has a markedly higher fat content than most other fruit, mostly monounsaturated fat, and as such serves as an important staple in the diet of consumers who have limited access to other fatty foods (high-fat meats and fish, dairy products). Having a high smoke point, avocado oil is expensive compared to common salad and cooking oils, and mostly used for salads or dips. The fruit is not sweet, but distinctly and subtly flavored, with smooth texture. It is used in both savory and sweet dishes, though in many countries not for both. The avocado is popular in vegetarian cuisine as a substitute for meats in sandwiches and salads because of its high fat content.

For the record here is the percentage of fat by weight for each of the fruits listed in the question

Avocado 14.7%

Banana 0.4%

Mango 0.0%

Pineapple 0.0%

More Info: en.wikipedia.org