Because all of those "many other planets" you're talking about are orbiting OTHER stars . . . not our Sun . . . so they're not members of our solar system.
Our solar system has exactly (8) major planets, and about half-a-dozen dwarf planets that we know of so far, including Pluto.
The Kepler Space Telescope, launched in 2009, dug up enough information to indicate the existence of several hundred planets orbiting other stars.
The James Webb Telescope will give us THOUSANDS more, if they ever get that thing off the ground.
