Amateurs who try to build their own explosives usually either fail to explode or explode killing the builder.
An older friend of mine at Boeing told me how when he was a teen, he had a teen friend who built a pipe bomb. They drove off to a field to set it off. It didn't explode, so his friend went to investigate. Then it went off, and my friend had the pleasure of driving his gutted friend to the hospital to die.
There's a selection process at work where smart people who know what they're doing don't try to assemble bombs in their garage for fun. If there's a legitimate reason like your country is fighting an existential war the kinds of people who can do things start doing things.
But it's just rare having a person smart enough to be able to do it be stupid enough to try. (and the people who do are nutjob terrorists like Timothy McVeigh)
FWIW, McVeigh got a lot of the technical details right, including many non-obvious ones. That was a sophisticated attempt by someone that actually knew what they were doing. It goes a long way toward explaining why that particular bombing was so effective.
That said, plenty of extremely smart people assemble bombs in their garage for fun. It is almost a rite of passage, at least in the US. The fact that historically you could just buy the common stuff incentivized smart people to attempt more technically difficult things for bragging rights. Most people have no concept for how available legal high explosives are in the US, even after 9/11 made it a bit more difficult.
An older friend of mine at Boeing told me how when he was a teen, he had a teen friend who built a pipe bomb. They drove off to a field to set it off. It didn't explode, so his friend went to investigate. Then it went off, and my friend had the pleasure of driving his gutted friend to the hospital to die.