Basic, boring, line-of-business web application shops are asking candidates to implement Boyer-Moore and k-d trees. When the applicant is going to be hired to mostly update JSX templates and figure out why the customer is frustrated. It's like every business needs Olympic athletes when they're running a hot-dog stand.
It's one thing if your business is writing a RTOS for a custom platform you develop. Asking a candidate to implement a slab allocator might be a fine exercise. It fits the work being done.
Businesses need to get off their high horse and look in the mirror. Most of them are doing mediocre things that need average, good-natured people who are willing to work.