Why do we square time?

Why do we square time when the curve looks “quadratic”. Sometimes the rate of increase of the dependent variable is not constant. If it is constant, then we have a linear trend. We can model that with a straight line and use Ordinary Least Squares . But sometimes the dependent variable is increasing/ decreasing  more rapidly as time goes on. For example, if your pay increased by 10% every month, you would soon be very rich. If we square time, the variable on the horizontal x axis, we can capture this effect. Example: you square ‘2’ and get ‘4’ which is only twice as big. You square ‘10’ you get ‘100’, which is ten times as big. Squaring time accommodates the increasing rate of change.