Lots of things work better in radians: s=r * theta, area = 1/2 theta^2 * r, d(sin(x))/dx = cos(x) (etc, for slopes and numerical algorithms), simpler series ap

Lots of things work better in radians: s=r * theta, area = 1/2 theta^2 * r, d(sin(x))/dx = cos(x) (etc, for slopes and numerical algorithms), simpler series approximations and algorithms for computing these and other functions, movement rates of things using gears or wheels are simpler to calculate, radians are dimensionless whereas anything else is not (when used in nearly any physics or math uses), hardware support for lots of related functions, interoperability with legions of existing software, papers, book, and algorithms...