Why should we generalized instead of specialized

Why should we generalized instead of specialized?

Sense from:
Operating manual for Spaceship Earth
Buckminster Fuller
Page 40 - 41
Arkana
ISBN: 0140194517

A type of bird which lived on a special variety of micro-marine life. Flying around, these birds gradually discovered that there were certain places in which that particular marine life tended to pocket-in the marshes along certain ocean shores of certain lands. So, instead of flying aimlessly for chance finding of that marine life they went to where it was concentrated in bayside marshes.

After a while, the water began to recede in the marshes, because the Earth’s polar ice cap was beginning to increase. Only the birds with very long beaks could reach deeply enough in the marsh holes to get at the marine life. The unfed, short-billed birds died off. This left only the long-beakers. When the birds’ inborn drive to reproduce occurred there were only other long-beakers surviving with whom to breed. This concentrated their long-beak genes.

So, with continually receding waters and generation to generation inbreeding, longer and longer beaked birds were produced. The waters kept receding, and the beaks of successive generations of the birds grew bigger and bigger. The long-beakers seemed to be prospering when all at once there was a great fire in the marshes. It was discovered that because their beaks had become so heavy these birds could no longer fly. They could not escape the flames by flying out of the marsh. Waddling on their legs they were too slow to escape, and so they perished.

This is typical of the way in which extinction occurs through over-specialization.