Why is the shape of the magnetosphere not spherical like the shape of Earth?

The Solar wind pushes the magnetic field that faces the sun and compresses the outer magnetic boundary. So it is distorted due to the magnetically charged, high velocity wind blowing out of the star.

Explanation:

Magnetosphere is the region surrounding the Earth that protects the Earth from the solar wind. It actually acts as a protective shield for the planet, from extra planetary hostile conditions.

Solar wind is the stream of particles that flow outward from the sun. These particles, basically electrons and protons, are highly energized and blow at very high speeds, at almost 1 million °C.

This magnetic region deflects the incoming charged particles, like those coming from the solar wind,

The shape of magnetosphere is not spherical due to solar wind.

Explanation:

A Magnetosphere is area around the planet which is regulated by magnetic field of earth. The shape of magnetosphere is result of impact of solar wind. The solar wind compresses the sun facing side of magnetosphere an approximate distance of around 6 to 10 meters. The solar wind elongates the the magnetosphere area/space which is away from sun (part of magnetosphere which is not sun facing).

solar wind is charged particles which originated from sun.