What possible purpose did the people have in mind, when they did this?

Could there possibly be any legitimate explanation?

Simply put: Bossism.

See, folks long ago amended the constitution to stop the inherent corruption of the big city machines.

Whether the original method for selecting senators is the correct one or not, the point is that monkeying with the Constitution can and will have unintended consequences.

Consequences that people don't think of, when they want to change this or complain about that... even if they feel justified at the time.

(think term limits, all that populist stuff)