What's Preventing Another Lost Decade for Equities?

If you bought at the peak of SP500 in 2000, it would take you almost 13 years to get back to the same 1500 level.

Your return is nearly 0% for 12 years. Maybe \~1% considering dividend compounding.

That remain the worst 12 year period for equity markets ever in recent years.

Not saying we are in the dotcom bubble as earnings/revenues are strong, but valuations are high if you look at CAPE ratio, it's the highest ever.

Why do people feel another lost decade won't ever happen again?