Not entirely sure how you might have reached that conclusion. Anyone dedicated to their craft will naturally --out of sheer interest-- devote time and effort to getting better at it.
For example, as a young EE I was constantly reading data books (yes, physical data books) and application notes. I had hundreds of data books and probably went through all of them twice and some several times. I could, at the time, talk about almost any chip from any of the major manufacturers and knew where relevant application notes existed for most problems. My employers did not mandate that at all. I was truly interested in what I was doing.
Someone interviewing me at the time would have learned a heck of a lot more about me if they asked me something as simple as "Can you tell me about a few interesting chips and how you would use them?" rather than asking me to design a low pass filter with a given frequency response using a specific op-amp.
The deep dive I am talking about does not require anyone disclosing code done for their existing employer. Nobody wants that.
Frankly, I would also want to know about life outside of work. However, given our laws you have to be very careful about how you might probe for such information. I feel very strongly that our legal system has, to one degree or another, sapped all humanity out of our work life. I've worked in other cultures where it is perfectly normal for people to greet each other with a kiss on the cheek and a hug or pat on the back in the morning. In the US almost any physical contact can land an employer in court and a manager in serious legal trouble. But I digress.