Many airlines and hotels provide different prices on different sites. Maybe the idea is to limit how many they sell at the lowest price.

With some airlines, the airline's own web site will have low prices not available elsewhere. I have found really low ex-India prices on CX and AI web sites that were not available from other sources. In other cases (e.g. AA), the airline's web site will have higher prices, with lower prices elsewhere. It's impossible to know what the airline's revenue maximization algorithm is. Just because it was cheaper in one case at one point in time does not mean it will be cheaper in general.

Sometimes (but not always) Kayak ferrets out the lowest price. The fact that airline prices are not transparent is the reason Kayak exists.