Ok, it seems you know more than me about this so let me try to poke holes in an attempt to learn further.

Was there really more capital available in private markets before 2008? I thought that was just because of post-2008 QE. That timing doesn't seem to work either.

Didn't Microsoft have billions in cash on its balance sheet in the 90's? I thought tech companies always hoarded cash when they were cash cows, and that it was at least partly a consequence of tax regulation, with cash sitting in one jurisdiction (say Ireland in recent years) costing too much to move around.

The fact that the delta in IPOs went up doesn't necessarily seem so indicative. There's a holding capacity for IPOs in an economy. I think your graph shows just how far the holding capacity dropped after SOX.