I hear this so often.. people are fine and happy on their meds and they arbitrarily decide to stop them. Why?
In lots of cases, because they're not actually fine and happy on those meds!
Psych meds aren't magic drugs that take away symptoms to cure someone, for the most part they just sedate you and suppress symptoms by virtue of that sedation - but also make you feel like a zombie and make it difficult to feel part of the world or that your life is meaningful.
Psych meds are not equivalent to insulin for diabetes or antibiotics for a UTI, for example.
Some people find them helpful and are prepared to tolerate all the down sides, some people find them helpful but not enough to justify the side effects, and some people just find them damaging.
Even for those people in the first category, some still make the choice that they want to use other methods of managing their symptoms or improving them.
For lots of people, their symptoms arise from underlying trauma. If that's the case and all you've received is medication that sedated you to make you seem acceptable on the outside, but doesn't stop your trauma from eating you up on the inside, would you really view that medication as helpful?
Or would you want to explore ways to address the trauma/underlying cause of your symptoms (it's not all "chemical imbalance")? Would you want to find ways to feel part of the world or would you want to exist in a fog? Would you want to feel like "you" and be able to hear your own thoughts clearly, or would you want to feel like a zombie?
A few legal caveats apply, but for the most part people are free and should be free to make the choices that are right for them about medication.