U235 is much easier to produce than plutonium.
There is a reason that China’s first bomb, South America’s bomb, India’s bomb, and Pakistan’s bomb were EU.
The primary benefit of a P239 bomb is they can be much smaller and boosted with fusion. If you goal is to blow up a city, you don’t need tactical weapons, just strategic.
Hence, why counties that have need for tactical nukes (e.g., US, Israel (shh!), England, and Russia) are the P239 business.
The arabs just want to nuke whole cities.
As I understand it... plutonium is a waste byproduct of light water and (esp.) breeder reactors. The primary challenge with plutonium is it cannot be processed like uranium, which which when bound to florine produces uranium hexaflouride gas suitable tor the centrifuge. The presence of plutonium240 interrupts the nuclear chain reaction because of high spontaneous fission rate (more neutron activity), thereby increasing risk of spontaneous detonation - a Bad Thing :-)
That's why Pu needs the implosion mechanism.
The Arabs/Koreans/other nuclear yahoos should be well-served with the U235 gun mechanism (and would of course be well-served by our assymetrical retaliation using U235 and Pu239-derived weapons).