Because it’s expensive. Even if we were to launch all of our trash using the world’s most cost effective rockets which takes $90 million to launch and can carry up to 70 tons of material into space, a year’s worth of trash could cost more than 6 times the world’s current debt. You would also need 18.3 million rockets to do it.
ScienceSwitch 
Launching our trash into the Sun would cause a loss of Earth mass, altering our orbital distance from our only heat source. This might be catastrophic or life saving, depending on the speed of our planet’s cooling vs. the eventual expansion of the Sun into a red giant. It might kill us, or be our only hope of survival.
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You ruined my 80’s 3rd grade science project. Hope you’re happy.
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Sorry, man 😦 😀
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