We tested the plutonium bomb only for a couple of reasons, we had more refined plutonium, and the gun-type uranium bomb had a much higher degree of confidence as it was so simple and stable. Agreed, the complexity of detonating an implosion type bomb has really stymied all who have tried.
Strange thing to say. Noone who has attempted to build an implosion bomb seems to have failed. And only the US and South Africa have even bothered with the gun-type.