It takes years to construct them and hundreds of thousands of people working on them, its a really big undertaking. The ones that reuse first stages can only do so a dozen times at most before its too fucked to use or misses a landing. Compare the ideal 30 tons or so per launch to the sheer mass of human waste and youll see space is not a solution for our trash, or even a small fraction of our most hazardous industrial waste (which is coincidentally extremely heavy material). Another issue is if you just place it in low earth orbit, it will be coming back down in a century, and if you place it in a higher orbit or send it off into solar orbit, youll drastically reduce the mass per launch making it an even more expensive undertaking.