In the section about Orbit and Environment the Wikipedia article about the Juno spacecraft says:
In comparison, Juno will receive much lower levels of radiation than the Galileo orbiter at its equatorial orbit.
The reason is partly because Galileo had a more equatorial orbit, in order for it to execute a large number of close flyby's of the Jovian moons for data collection. Juno carefully avoids that by remaining in an essentially polar orbit that mostly avoids the intense radiation belts, at least in the beginning of the mission.
Galileo operated for roughly seven years. It was inserted into Jupiter orbit December 1995, the camera operated until January 2002, and the spacecraft was de-orbited - still under control - in September 2003.
If Juno will receive less radiation than Galileo and yet it's systems will start failing within a few months and it seems mostly within one year, even with the electronics in a titanium radiation vault, why would it fail so much faster?
My guess is that it's a side effect of Moore's law. Pixels are much smaller, and transistors are much much smaller 20 years later, perhaps 100 to 1000 times smaller volume per element, so while it's much faster and more powerful, it's much, much more sensitive to radiation. But that's only a guess.
If Juno will get much less radiation than Galileo did, why is it expected to fail so much faster?