When it was first planned the F-20 was known as the F-5G and was intended to incorporate the minimum changes needed to accept the new engine, so that older F-5 could be converted. By the time development was complete, there were so many changes that this was no longer possible. So bang went one possible market.
The F-20 was then in direct competition with the F-16, but the F-16 had the overwhelming advantage of having been bought by the US Government, so everyone wanted that instead. No-one wanted the risk of being the launch customer for a new aircraft like the F-20.
Pity really, it would have introduced an interesting new gun, the 'Tigerclaws', developed from the M39 to be much lighter and faster-firing.
Tony Williams: Military gun and ammunition
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