I haven't found one of Google's page one retailers who are lower in price than I am.
Price is not always such an important factor. It could be something else - delivery times, number in stock, product description, trust signals.
Perhaps a competitor has made improvements - not necessarily being better than you - but communicating one or more of this factors better than you to the customers.
In some niches there is also a reverse effect in prices. We lost a significant amount of sales for one of the luxury brands we sell when our competitors stopped offering discounts and raised the prices to the same level we sold for - the recommended retail price. Price can be a trust factor, too and being too much cheaper than the competition can raise suspicions.