Why was Weaver even targeted?
He was targeted because he was associating with criminal groups. The Aryan Nations was a meeting point for many white supremacist groups such as the KKK, the National Alliance, and smaller groups such as the Order. The Order was inspired by William Pierce's (of the National Alliance) the 'Turner Diaries' (as Timothy McVeigh would later be). The committed a series of crimes including a multi-million dollar armored car robbery. Randy Weaver hung around with these groups and was good friends with Butler (the Aryan Nations preacher) when he was arrested for attempting to conduct a terrorist attack against a gay bar (shortly before Weaver was arrested). The government informat was investigating the Aryan Nations, and although Weaver was not an offical member, he had deep ties to the group. He met with a government informat and spoke of starting a 'patriot' group similar to the Order.
The informant wanted Weaver to introduce him to one of Weaver's contacts in the KKK of a different state that was involved in a number of bank robberies (that is where the bank robbery connection got mix in with the FBI intelligence report). After the informant was exposed, they asked Weaver to make the introduction to the Klansman in exchange for dropping the gun sell charges Weaver had previously committed. Weaver refused, was arrested, didn't attend his court date (whether changed or not), and then made threats against anyone that might attempt to arrest him.