Casting, machining or welding plutonium into the right shapes and purities without killing your self, or some of the other exotic metals, without killing your self or making your neighbours sick in a sub 1-3 week horizon is incredibly challenging. The exact geometries you need to achieve aren’t easily available either neither is measuring is you achieved them without again killing your self. Getting a dirty fizzle is a lot easier which is why people are afraid of dirty weapons by terrorists.

I'm sure in 1985 plutonium was available in every corner drugstore, but in 2024 it's a little hard to come by.

[Cut to me in 1999 driving my old station wagon down to the local hardware store to pick up a few kilos of highly purified enriched uranium and some C4]

>> ,I'm sure we would've had terrorist attacks with nukes already. Or if terrorism was that big an issue

There are two problems with that statement. Let’s examine them

Firstly, does majority of terrorists want to nuke NewYork? If you gave 9/11 bombers a 5 megaton warhead, would they use it? You have to remember that many of them imagine they have a just cause.

Second, imagine you are could make a nuke at home and were completely immoral, who would you sell it to?

There are many evil governments and organisations that could pay more and be better clients than terrorists.

Chemical attacks, like one sarin attack in Tokyo by Aum Shinrikyo, are few orders of magnitude cheaper than any nuclear attack.

This is the same method published in the BBS/FTP distributed Jolly Rodger's Cookbook in the early 90s.