This is an interesting question. The answer might relate to secondary human rights associated with invention which might be explicable through hard work to create something new (perhaps applicable to Klein blue, but certainly not applicable in this case), the more disturbing psychological reasons exemplified by the rich mogul who buys a work of art and hides it away in a vault ensuring that nobody else can view it, or commercial reasons - it has fascinating properties and its use in his art work will in all likelihood enhance their commercial value (and possibly aesthetic value - that remains to be judged).
The immediate question was "how can he...?" or "what gives him the right...?". These are easily answered.
But "why did he...?" is a much deeper question that only Kapoor might be able to answer (or might not), and as yet he has not.