The most obvious example of this in daily life is through airlines, where the difference is pretty transparent and you get night-and-day better service by being a loyal customer.
With top status with AA and UA (EXP and 1K), you connected to U.S.-based very senior phone agents right away, who always make sure to take care of any issue that arises. 50min delay on your AA flight? No problem, sir, we are rebooking you on Alaska so you don't miss your dinner meeting. (Real example from last weekend)
Customers are put in different levels in the loyalty program, with the top level getting to pre-board the flight, getting free upgrades to any empty seat in business, getting many other extra perks that make flying a joy. You get a smile, a thank you, and a free drink when flying in the back. Within a status level, customers are oftentimes ranked by how much revenue they bring to the airline. (On AA, upgrades are ordered by Elite Qualifying Dollars the flyer has spent in the prior year)
Contrast that with the experience the vast majority of people have flying the very same airlines: say the words United Airlines to your average flyer and it brings back memories of Dr. Dao, of cramped seats in the back middle row, of not being able to bring a carry-on because they're in basic economy, of having to gate-check your bags, etc.
At the end of the day, frequent flyers bring the vast majority of profits to airlines, so it makes sense to focus all efforts on catering to them vs. the average person. The cheap seats have very low margins, oftentimes negative… so it just infeasible economically to give everyone good service.