it true most of Kuala bears die from starvation ...

Koalas can live as long as 17 years, however males life expectancy is less than 10 years (due to injuries during fights, dogs and cars). Females generally live longer. Koalas living in an undisturbed habitat would have a greater life expectancy than those living in suburbia.

Koalas have a slow metabolic rate due to their high-fiber, low nutrient diet. Because they store little or no fat, koalas must adopt strategies that conserve energy. Sleeping is one of them.
Koalas sleep for up to 16 hours per day in order to conserve energy.
A very slow metabolic rate optimizes its energy requirements and allows koalas to retain food within their digestive system for a relatively long period of time, maximizing the amount of extracted energy.

So according to most research they die of disease and injuries caused most commonly by dogs and cars. 

I found this interesting article that says :

"..Biologists have long used the degree of 'tooth wear' in koalas to assess how long they have left to live, but its relationship to koala sex habits had never been noted before. Koala teeth wear down as a result of their constant grinding of eucalyptus leaves, their primary source of food.

The blunter their teeth, the less food they can digest. Consequently, most koalas don't actually die of disease or old age - they die of starvation."