| "TBH I don't know why a giantic magnetic rail gun / catapult
| into space to shoot things up there hasnt been built yet."
To get into (and stay in) LEO, an object needs to be traveling at about 17,500 mph when it reaches its orbital slot.
A rocket gets there by starting off traveling slowly down where the air resistance (and hence friction) is heaviest and accelerates as it rises into less dense/less compressible/less friction-inducing atmosphere.
On the other hand, atmospheric friction and compression is used when decelerating out of orbit. This generates thousands of degrees of heat which needs to be dissipated/shielded against.
Now take your rail gun. Assuming as a starting point that it is long enough -- some number of miles maybe* -- that the acceleration to escape velocity doesn't pancake every structure in your launch vehicle and payload, there is still the issue that being at the bottom of a gravity well requires that your projectile be going at well OVER orbital speed when it leaves the muzzle.** Otherwise,just as with a thrown rock, gravity will start slowing it down as soon as the driving force is off. If it doesn't reach orbital height at orbital velocity -- just like that rock -- back to earth it falls.
So your railgun launcher has to -- slowly enough not to destroy the projectile -- accelerate it to something in the 20,000 mph range... at sea level... in order to still be at orbital velocity when it finally reaches its intended altitude... And once fired into flight, the projectile has to be sufficiently heat-resistant that it isn't instantly immolated by friction/compression-heated atmospheric values above anything that humankind has ever built. (Bear in mind that -- while, granted, its thermal protection had been compromised -- the temperatures and stresses that destroyed the shuttle Columbia happened when it was decelerating from the arbitrary "edge" of the atmosphere at 75 miles above sea level down to final breakup at about 40 miles up.)
...And you want to shoot your payload out of a cannon at HIGHER speeds than the Columbia was traveling, in atmosphere that is DENSER by a couple of orders of magnitude than she was traveling through, and hope to get it to orbit intact...?
Good luck with that.
A long-enough catapult might POSSIBLY be useful for accelerating something akin to a SCRAMjet to operational speed, which could then accelerate through much of the atmosphere before handing off to a rocket engine for orbital insertion, but a catapult to orbit setup without any other motive force...? SO not happening. And I see no way that a catapult/scramjet/rocket combination isn't going to be MORE complex and expensive than what we have now,
No, I'm afraid that (absent any completely new science like antigravity) until we get the first beanstalk built, rockets are pretty much going to be the only way into orbit.
* The difficulty of building a miles-long, precision-engineered railgun in an utterly straight line tangent to your starting point on the surface of the earth (You can't just put a ski-jump at the end if you're launching something at Mach 27 or so) is left as an exercise for the reader.
** Ditto the effects of a Mach 27 sonic boom on surrounding organisms and structures (including your miles-long, precision-engineered etc. etc.).