As others said, sometimes we are voting on a lot of offices and a lot of initiatives/propositions. A voter is in several different type of districts, and the boundaries often don't line up, so your neighbor may be in the same federal congressional district, but not the same state congressional district, etc. Commonly in California, I voted on congressional districts, water district, lower school school district, high school school district, community college school district, water district, sanitary district, flood control district, vector control district, county supervisors, and I wasn't even in a city to have city supervisors or mayor. Almost all of these electrions are timed together, in order to increase turnout and reduce the election expenses.
Ocassionaly, we have hundreds of candidates for one office (ex California governor recall replacement that got Arnold Schwarzenegger into office).