Kurzweil just says 2045, because that's where his chart or accelerating returns tells him it will happen.
> Such trend-curves... extrapolated 30 or 40 years they are so high and steep that even the most naive futurist discounts their accuracy.
(That's the closest therein to a specific prediction date, from 1983: https://imgur.com/a/HrUxGts)
> let me more specific: I'll be surprised if this event occurs before 2005 or after 2030.
From 1993: https://edoras.sdsu.edu/~vinge/misc/singularity.html
It's interesting that 29 years after he said that, and 8 years remaining on the timeline, it's not completely out of the realm of possibility.
If, say, I were to predict that 40% of intercity travel would be via high speed rail in 2100 in California, I should be able to either argue why high speed rail would spring out of nowhere in 2099 or have a plausible story as to how it might grow.
(2) Prediction on long timelines is too hard. It's more useful to generate ideas about possibilities. With the small samples here, people are almost just as likely to be lucky as right.
We saw a microcosm of this early in the pandemic, where some groups got really excited about forecasting the number of cases. (1) I didn't see anybody quantitatively evaluate their own predictions and own up to how good or bad they were. (2) Everyone pretty quickly gave up even trying to make predictions over a month away. It was too hard. So it devolved into fitting short-term curves and then I think mostly they gave up forecasting altogether.