agreed that more investors are crowding in
there are many other issues going on.
majorly: tech companies now dominate the indices. tech companies run far larger margins than the old line manufacturers and banks that used to dominate the indices. So it's natural that the indices will have higher multiples. Just because they have higher-margin companies in them, that can scale endlessly.
also, fundamentals have changed for the better
big companies can now sell overseas, expanding their markets by a massive amount and diversifying their customer base. That deserves a bigger multiple.
accounting rules have become tougher and cheating harder to do. Likewise, that deserves a higher multiple
accounting rules themselves have changed, making apples to apples comparisons harder.
we don't have a regular business cycle resulting in regular recessions anymore. We only get recessions from big incidents like covid, the great financial crisis, the dot com blowup. that deserves a higher multiple
tech has made companies far more productive and efficient
etc
point is that comparing valuation ratios from 50 years ago to today is useless.