Voter apathy in moderation is a fine thing in our Republic. Only the actually motivated (and hopefully informed and motivated) bother going to the polls. Their votes would mean less if the 17th were repealed, as their vote would only indirectly appoint a Senator, they would vote for a State Legislator who would (in back room deals) vote for a Senator.
The people are represented in the House. With the Senate also elected by popular vote, we have 2 chambers focused on vote grabbing through entitlements.
With a Senate beholden to a State legislator, the Senate would be beholden to the state. Since the state governments also want power, it becomes a balance between state and federal.