Tennyson had a super-long career and wrote a ton of poems, so we're not going to try to fit them all under one big umbrella. Let's just deal with the second half of his career, after he became the Poet Laureate.
Being England's Poet Laureate is basically a government job, where you become the country's official poet, and write poems for inaugurations, funerals, etc. It makes sense that the Poet Laureate couldn't be too "out there" and would want to take a traditional stand, both in his style and the issues he covered. In addition, Tennyson was a really popular, widely read poet by this time, and readers appreciated a fairly steady, calm approach. That's not to say that he couldn't be exciting or fierce or interesting at this point in his life, but he generally wasn't experimenting too much with style or subject matter.