I don't think anyone is buying any "new" C/D models. Presumably you mean E/F.
There's a reason they're doing this - the average remaining frame life for the 460 or so C/D across the combined USN/USMC fleet is in the hundreds of hours. They've been spending on structural mods to get another 2000 hours out of them and have been for some years, to the tune of $2.7Bn or so.
Nor are "all" the USMC C/Ds going to have their APG65/73 replaced by AESA. The RFI is for 98 kits (7 sqns worth) and adding 98 AESA kits to that total is probably largely offset by savings in not having to support 65/73.
A bit of context from the actual budget materials usually puts these things in perspective.
Last edited by Not_a_boffin; 22nd Mar 2018 at 12:28.