These plants are not grown the way real Bonsai are and usually live just long enough for you to think you did something wrong instead of understanding you just bought a bad product.
That's the catch.
Guilt.
When bought, you never know if it was just repotted, if it was a greenhouse plant, if it was originally in the ground.
It's already doomed when bought.
Then, after a while it turns brown and dries up.
Not your fault. It's the vendor's trick to keep selling more plants.