How many breaches in security can be attributed to humans vs. technological weak links?

Even 10 years ago the answer was the same. Humans are always the biggest security risk. But we have to identify what we can change and what we can not. For example 2FA. The majority of people won't use it because they don't understand what it is, how it works, or how to set it up. But if providers made 2FA the standard and provided an Opt-out option see a much higher percentage of user adoption and retention (SANS STI study).

How many breaches could have been stopped if 2FA was enabled by default? According to this chart: http://www.informationisbeautiful.net/visualizations/worlds-biggest-data-breaches-hacks/ in 2014 (around the time Banks started mandating 2FA for "new" computers) overall large scale hacks decreased.
Only the amateur goes after the computer. The professional goes after the individuals.

Definitely the human factor is to blame for most of the security issues today. Social engineering and the lack of education and awareness of the users has a lot to do with many of our cybersecurity incidents.

The human factor is highest.