There are so many software engineering candidates who literally cannot write the simplest code. I even had someone actually say "I don't really write code at my current job, I'm more of a thought leader." Bzzzzzt.
I've always prepared what I called level 1, level 2, and level 3 questions ready for candidates. But, I almost never even got to level 2, and never in 20 years of interviewing got to my level 3 questions.
I've been around the block for over 3 decades. I've had a number of high level positions across both IC and management tracks. These days I'm very hands on keyboard across a number of clients. If you asked me to write a basic for loop or if statement, there's a small chance I'd flub the exact syntax if writing on a whiteboard. Both because I bounce between languages all day and wires get crossed on the fly, but also the standard interview pressure type arguments. Whereas if the test is "does this person understand what a for loop is and how it works?", then yes, I can easily demonstrate I do.
In real life I'm not going to take an interview where there's not already that degree of trust so if that questions comes up something is already wrong. But I'm sure there are interviewers in the world who'd fail someone for that.
One of the worst guys took 20 minutes, with me having to coach him through it the entire time. It was a true exercise in patience, but I don't mind helping people learn new things. When he got his rejection email, he actually complained to the recruiter because he thought he did really well. Dude...
Half of the people I screen fail it. It's crazy.