Because?
Last time i´ve checked the development of every radar linked to AEGIS starting on AN/SPY- 1 going to AN/SPY-7 was heavily funded by the Pentagon, APAR by the Dutch, German and Canadian MOD´s, Seafire by the French DGA, the Kronos family by the Italian Navy, Ceafar/Ceafar 2 by the Aussie one, etc, etc...
If you want a particular system with specific capabilities and have a preference for home grown development (and i really dont need to explain why the UK, or France, US, Australia, etc, might prefer to develop and produce their own high end military sensors, right?) you have to pay for it.