Specialists are more likely to go extinct.

A specialist is optimized for their niche.

That allows them to outcompete others in their niche, but be worse than others at competing outside their niche.

That means that specialists are less able to handle the disappearance of their niche.

A generalist (especially one that has a low caloric need, due to small size or metabolic rate) is more resilient; more likely to be viable no matter what happens in the environment.