The whole point of a rotary encoder is that it ISN'T position oriented. If you want to have a control that's positional, use a potentiometer. Encoders simply give you pulses to tell you that it's moving in one direction or the other.
You seem to lack a knowledge of what a rotary encoder is.
Encoder means any one of a number of technologies for detecting position or change in position, here rotary position.
You can get analog encoders, digital encoders analog+digital encoders, incremental encoders, absolute encoders and
incremental encoders with index pulse. Rotary and linear encoders both come in absolute,
incremental and incremental with index pulse forms.
An absolute encoder returns angle directly (many give you the turn count too, some are
accurate to millions of steps per revolution). They can be expensive or extremely
expensive.
Incremental encoders are generally cheaper, but the ones which generate an index pulse
can be used as absolute position sensors once calibrated.
Incremental encoders require constant attention to maintain a position / angle value,
which often means interrupt handler is used to let that all work in the background.