Because "achieving goals" subsumes "making predictions". Remember, Russell's goal is to find a definition of intelligence that is broader than humans -- and even broader than sentient beings. But using the "achieving goals" definition, one can include system that accomplishes goals, even if we can't find any way to verify it is making predictions. For example, even a purely reactive agent (e.g. operating on instincts) can display intelligent behavior if its actions serve its purposes.

If you are seeking one clear point of view about the nature of intelligence, I highly recommend Russell's writing. You don't have to "agree" with his definition, especially not at first, but if you give it a fair reading, you'll probably find it to be coherent and useful for the purposes he layes out.

Russell has been thinking about and teaching these topics for probably 40+ years in depth. So it is sensible to give his ideas serious consideration. Also, there are scholars who disagree with Russell's definition or accentuate different aspects. Wherever a person lands, these various scholars provide a clear foundation that is all too often lacking in everyday conversation.

Not really, but I can see why you might say this. Neither Russell nor I are attempting to define "the one component" of intelligence -- we're saying that there is no single kind of intelligence. Only when one defines a particular (agent, environment, goal) triple can one can start to analyze it statistically and tease apart the related factors. You and I agree that the result will be multifaceted.

I wouldn't say I'm trying to "reduce" anything. I would say I've been attempting to explain a general definition of intelligence that works for a wide variety of types of intelligence. The goal is to reduce unnecessary confusion about it. It simply requires taking some extra time to spell out the (agent, environment, goal).

Once people get specific about a particular triple, then we have a foundation and can start to talk about patterns across different triples. If one is so inclined, we can try to generalize across all intelligent behavior, but frankly, only a tiny fraction of people have put in the requisite thought to do this rigorously. Instead, many people latch onto one particular form of intelligence (e.g. abstract problem solving or "creativity" or whatever) and hoist these preferred qualities into their definition. This is the tail wagging the dog in my opinion. But this is another topic.