What period are you specifically referring to?
I assume you mean western/European bathing practices over the past few millennia. In which case it's not true that people bathed once a year.
People in the past thought and acted much like people think and act now. We are repulsed by foul smells, we evolved that way to detect rotten foods and other unsavory things that we don't want to ingest. Bathing was a common occurrence in ancient Greek and Roman culture, I can't speak too much about other regions. People tended to bathe or clean thoroughly clean themselves every few days, and for the most part at least once a week. The Romans were absolutely obsessed with baths, hence why they built so many massive bathing complexes.
Bathing began to change once the western empire fell, but it still stuck around. The massive baths ceased to be maintained but smaller scale baths continued to be used.In some instances the church was against bathing, as many of these smaller bathhouses doubled as brothels or simply attracted prostitutes, but considering we hear about the church complaining of the continuous existence of bathhouses for several centuries, it's safe to say they stuck around.Another thing to note is that before modern germ theory the idea that disease spread through miasma or bad air was both the social and scientific norm for much of Europe. Keeping clean, and not smelling horrible, wasn't just courtesy, it was how people thought they could stop the spread of disease or prevent it.
Cultural and demographic changes would make bathing far less popular past the 14th century in much of Europe though. After the Black Death bathing began to be viewed with suspicion not just by the church, and medical manuals started to write about how bathing spread illness. The idea that bathing opened up your bodies pores and allowed disease to enter caught on. In addition to this clothing changed, from being primarily made out of wool to linen. Linen was much easier to clean than wool, and so one no longer needed to bathe as often to appear clean, if they washed their clothes frequently enough. It was common to simply wash your hands, arms and face, whatever is visible and only clean the rest of your body during far less frequent baths. It became more common to bathe only once every 2 weeks to once a month during the 18th century. Hope this helps.