Why does the Nobel committee not award prize to collaborations?
In paragraph 4 of the statutes, it restricts the price to be only awarded to two works and to a maximum of 3 individuals.
But it also says, that it can be awarded to an institution or organization. Which has been done with the Nobel Peace Prizes to the EU.

A prize amount may be equally divided between two works, each of which is considered to merit a prize. If a work that is being rewarded has been produced by two or three persons, the prize shall be awarded to them jointly. In no case may a prize amount be divided between more than three persons.
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Each prize-awarding body shall be competent to decide whether the prize it is entitled to award may be conferred upon an institution or association.