Binary is unambiguous. Thinking of a physical representation could be a series of valves with fluid flowing through them. 0 = valve shut tight, 1 = valve open. You could make a “computer” with a bunch of valves. But introducing the 2 brings confusion. Assume 1 = valve half open, 2 = fully open. If a valve needed to switch from 0 to 2, there will be a certain amount of time that it is being registered as a “1”. Valves at different parts of a network will have different flow rates, and a fully open valve at point A might have the same flow rate as a half open valve at point B. Meaning the same “valve sensor” could not be used, because if that sensor was programmed to use valve A’s full/half flow rates, putting it at valve B would yield different values than expected.

Theres a lot more factors why trinary isn’t used for computing, but these give you an idea.