If they wanted to amend their state constitutions, they would have amended their state constitutions.
The US Constitution already delegated limited powers to the newly formed federal government. The purpose of the constitutional convention that incorporated the Bill of Rights was for clarifying federal and state powers, and also for clarifying rights retained by the people (not just the states).
During the process, some restrictions were specifically imposed on Congress; other rights of the people were asserted as declaratory rights that may not be infringed. Unless the participants of the convention were stupid (which you have already argued they were not) this distinction of declaratory rights and restrictions of congressional powers was done for a reason. There was no need to amend state constitutions.
It wasn't done by the Framers. Maybe by you.
Exactly. Well said...