Why Computers Use Binary, Not Decimal
Computers use binary because their underlying hardware — transistors and digital circuits — is built to reliably distinguish only two clear states, typically represented as a high or low voltage (on or off), rather than ten finely graded voltage levels a decimal system would require; binary's two-symbol system maps directly and robustly onto that physical reality, which is why it became the foundation of digital computing rather than a design choice made for human convenience.
This is a hardware-driven decision, not an arbitrary mathematical preference — decimal computers have actually been built experimentally, but never achieved binary's reliability and simplicity at scale.
Why two states are more reliable than ten
Distinguishing cleanly between two voltage states (on/off) is far more resistant to electrical noise and component variation than reliably distinguishing between ten finely spaced voltage levels — a small fluctuation could easily misread a decimal digit, while binary's wide margin between its two states tolerates much more real-world electrical imperfection.
Where humans still interact through other bases
As covered in the positional-systems guide, programmers commonly use hexadecimal (and sometimes octal) as a more compact, human-readable stand-in for binary, since it groups binary digits neatly — the computer still operates in binary underneath either way.