The reason people are shocked isn't that VCs are willing to take a risk on an idea that appears ridiculous at first blanche, it's that Juicero had 4 rounds of investment before they launched, which amounted to $118.5M. That includes a $70M Series B in 2016-03 which was quickly followed by a $28M Series C one month later. [1]

Few would be surprised by a few million being spent looking for a market fit on a wacky idea, it's the scale and obvious demand to get involved at such a late stage.

[1] https://www.crunchbase.com/organization/juicero#/entity