Almost everything is made of a combination of known things and, as @EricShain said in a comment what is obvious now might not have been obvious then. More importantly that the number of years that has past is the fact that we know about intermittent wipers. Humans have a tremendous hindsight bias. Once you know something, it seems obvious. It is very hard to put your mind into a state before you knew something.
That is why, until a few years ago, we had the TSM rule for judging obviousness. Teaching Suggestion Motivation. To find something as obvious the examiner needed to cite a teaching, suggestion, or motivation to modify or combine the prior art teachings to achieve the claimed invention.
The Bilski v. Kappos (2010) case said that TSM is an ok guideline but no longer required to make a good case of obviousness. It makes obviousness arguments harder. The examiner, however, is still not allowed to say "seems obvious to me". They must find a set of previous work that collectively have all of the elements of the rejected claim and make a reasonable argument that someone would be motivated to combine each of then to get to the claim as a whole. It is the arguments that someone would quickly jump to combining them that got easier for the examiner due to Bilski.