It's far easier to change a state government than it is the federal government. The states used to be able to recall Senators if they failed to do their jobs correctly; as determined by the elected body within the state. It's simply a single level indirection of Democracy. The House of Representatives is direct. This was intentional.

What's "indefensible" about this?

And you can amend how the body is elected; hell, you can amend how the president is elected. Also Article V provides for a state "constitutional convention" as a process for initiating changes, bypassing both the Senate and the House.

For that matter, you could amend the Constitution to change the process for amending the Constitution, even to eliminate the possibility of future amendments altogether.