They can't just install the old radars as the airframe has been structurally modified and is no longer compatible.

MD @distant_earth83
11 Feb 2026 · 11:20 PM UTC
https://nitter.net/distant_earth83/status/2021725955362848976

A photo of the same ballast weight that Lockheed Martin has been installing
since June 2025 on F-35 fighters delivered to the US armed forces, instead of
the new Northrop Grumman AN APG 85 onboard radar, which still has not entered
serial production. The image shows a US Marine Corps F-35B.

Previously, F-35 aircraft were equipped with the Northrop Grumman AN APG 81
radar, which continues to be installed on all export versions. Right now,
aircraft fitted with the AN APG 85 are expected to start entering service only
in 2028.

t.me/bmpd_cast/25075