He did write extensively on many topics. The volume Ideas and Opinions contains a wealth of articles, letters, editorials, speeches, and so on that he gave on philosophy, religion, politics, and numerous other topics separate from physics and mathematics. So the idea that Einstein would have deep opinions on many things other than, say, General Relativity, is not ill-founded. During his life, especially after he moved to the United States, his opinions were routinely solicited by newspapers and magazines, as he became the stand-in for "the smartest person alive." And both during and after his life, "Einstein witticisms and jokes" became a common staple of people's memories of him.

Which is just to say, it's not a crazy thing that he might have had a lot of varied opinions. He wasn't as "constrained" as some famous "geniuses" have been.

That being said, a lot of the fake quotes attributed to him are pretty banal, and he was never banal.

I don't think the above answers adequately address your question. Einstein became a celebrity soon after arriving in the U.S. and was constantly hounded by the press. Over time he came to enjoy the attention somewhat and ascertain how best to respond to it.

In his recent biography of Einstein, "Einstein, His Life and Universe", Walter Isaacson wrote:

"Einstein had just the right ingredients to be transformed into a star. Reporters, knowing that the public was yearning for a refreshing international celebrity, were thrilled that the newly discovered genius was not a drab or reserved academic. Instead, he was a charming 40-year-old, just passing from handsome to distinctive, with a wild burst of hair, rumpled informality, twinkling eyes, and a willingness to dispense wisdom in bite-sized quips and quotes."

We can get idea of Einstein's own reaction to this attention via the novelist C.P. Snow who got to know him well:

"There was a streak in him that enjoyed the photographers and the crowds, He had an element of the exhibitionist and the ham. If there had not been that element, there would have been no photographers and no crowds. Nothing is easier to avoid than publicity. If one genuinely doesn’t want it, one doesn’t get it.”