Why A Probe, Rover Need To Throw Away Their Stages Of Space Rocket?

 I do not think spacecraft, space probe, space rover need to do so after they use solid fuels exactly like the space shuttle, read my writing about space shuttle: https://shuyingwritings.blogspot.com/p/rocket-sciences-future-space-shuttles.html

Universities by some countries with space stations can have  rocket manufacturing companies like universities sharing three space rocket manufacturing companies which one of it funded by their government of their country another two funded by private entities, which will be the sponsor. Their tasks are to figure out why the space probes keep bound by gravity and orbits of other planet and unable to get further from milky way, to edge of universe, to other further star, planets not in milky way. Another task is to study solid fuel for rockets and manufacture different rovers, probes, spacecraft or other man made space objects, space study equipments which can help their government, to be sold to some private sector, consumer and others. The universities can use the space rockets, products they manufactured for universities research usages. They can create other products just for universities usage in their three rocket manufacturing companies. The universities in the three rocket manufacturing companies need to study method, the solid fuels for rovers, spacecraft, space probe to reach further than milky way, edge of universe, far places in universe in less than a day, less than a week and help goverment, private sector, consumer, others to make those rockets which reach further than milky way, edge of universe, far places in universe in less than a day, less than a week. I also like space lecturers to give some space speeches, talks about space like sharing sessions about researches with speeches, talks like stephen hawking, famous space professors.

Question:

What if the planets which wait to be explored have unknown weather?

Usually people will take metal space stations(which can stay in orbit)  place them on orbits of planets, other places with orbit, then place weather equipment , temperature measurement on ground of the planets to study , study from space station windows facing bottoms to the planets with zoom function camera,  binoculars(choose the range) . Then only start observatory on ground of the planet, placing human and living place on planet. Another function of this space station is to look at space rocket and space rocket testing so that space rocket can increase speed and leave orbits, gravity, you can do like car testing like car testing, the ways they steer the space rocket with remote control from space station, others, skills of steering space rockets.Usually if they are remote controlled you need to search method to connect the remote control signals such as connected by several satellites with propulsions, just like the space rocket drop the each of the satellites into its pathway and arrive at its destination.