Incentives are different too. Outside of highly fundamentalist cultures, there isn't really a strong benefit to a family from pressuring someone to keep a child. In developed countries, children are a huge liability for the first ~20 years of their life. Meanwhile, with assisted suicide, there are strong incentives around cessation of ongoing medical care (costs), and obviously inheritance.

Between that and possibility of presenting some murders as assisted suicide, I think if the idea is to be implemented, it really needs to be done extra carefully.