That's easy. It's due to a psychological concept called: transfer of learning [0].

Perhaps the most famous example of this is Warren Buffet. For years Buffet missed out on returns from the tech industry [1] because he avoided investing in tech company stocks due to Berkshire's long standing philosophy to never invest in companies whose business model he doesn't understand.

His light bulb moment came when he used his understanding of a business he understood really well i.e. their furniture business [3] to value Apple as a consumer company rather than as a tech company leading to a $1bn position in Apple in 2016 [2].

[0] https://en.wikipedia.org/wiki/Transfer_of_learning

[1] https://news.ycombinator.com/item?id=33612228

[2] https://www.theguardian.com/technology/2016/may/16/warren-bu...

[3] https://www.cnbc.com/2017/05/08/billionaire-investor-warren-...