Honestly this is probably because other businesses started doing it. When businesses have no clue they look to the market for the "standard" way of doing things. We don't make mechanical engineers design mechanical solutions for fun.It is just a consequence of the early culture of "hackers" and people who do that stuff for fun and for work. Hopefully dies over time, but it is unlikely given that now seems like the standard thing to do. Businesses are not rational thinking creatures. They just do what feels like lower risk if they can.

Leetcoding involves preparation for known problems and churning out solutions in least possible time. Most of the business have problems along the same lines (think of CRUD, authentication, authorization, UI animations etc ...) and they think people who excel in the former might do well in latter.

Edit: better sentence formation.