Witnesses were paid much more before Hardfork 16. It was a unanimously popular decision to control inflation and make the Steem token more attractive to traders. Witnesses, Steem Power holders, the general reward pool alike took a pay cut, to limit inflation under 9%. All I'd say is, witnessing is a political position, and you have to campaign diligently to get higher up the ranks. It doesn't come for free, nothing does.

As for the multiple reward windows, it's not actually a question of having more witnesses, but rather runaway computational costs for each witness. I'm not a developer, so I don't know the exact details, but you can track down the GitHub issue for that to the know the exact reason why this decision was made. It was part of the Hardfork "Simplicity". 0.17.0 and 0.18.0, I think.