Good point. I assume one also needs two antennas to take advantage of diversity reception? One would need a lot of real estate for TWO 160m antennas
In fact many 160M receive systems are rather small (see e.g. K9AY, Hi-Z) and the null off the back of typical 160M receive loops is very very deep.
One common setup, is to use one steerable directional receive antenna on second receiver, and the transmit antenna (presumably non-directional) on the main receiver. If something is heard on the non-directional antenna not copied by the directional, time to swing direction!
Other times a station might have a really good beverage but only for one or two directions. The monster stations have multiple arrays of beverages!