Crux of the problem: voting bots give predictable ROI, curation doesn't (at least the way the voting window algo works right now)!

If I have lots of SP, why would I waste my precious time curating when I can just passively delegate my SP and collect a steady and predictable income.

You can play with the curator/author reward percentages all you want, the outcome will be the same. Full-time curators with large SP will want a steady income for their time spent on this platform, or else they go to the bid-bots or spend their $ on other coins.