Here's a little bit of history for you. There was a time, when electronics were just resistors, vacuum tubes, capacitors, etc. Clever people built different things, like light bulbs and electromotors. However, the problem was, that logic, like math, was really difficult to map, especially since signals weakened in circuits. Materials at the time weren't as pure and refined as we can make them today, so some rough way to tell defined signals apart had the be developed. The idea: establish voltage-levels to transmit different information. For example 0-1V: 0, 1-3V: 1, 3-5V: 2, etc. Systems like that were created (see trinary logic a.s.), but soon (very soon) afterwards, people found out that they are difficult to work with (logic-wise and because the voltage is not stable at all). So they decided to simplify the whole idea: There should only be two levels - ~0V and anything else.
We could, in theory, go back to more than those two levels, however more levels means a nonlinear increased complexity. At the moment companies try to slowly tackle that problem. SLOWLY. For example, Samsung is experimenting with TLC NAND SSDs, which can store three bits per cell (8 levels). The first consumer SSDs with this technology were the 840 series. Another example for multi-state information handling are Qubits, which can store up to two bits (4 states) of information per Qubit. As you know, however, quantum computing also still is in its early stages.