If you pay for a reddit premium subscription, you get a number of benefits. The main ones are highlighting new comments since you last viewed a post, and removing at least some ads. It also gives you a monthly allowance of "reddit coins" that you can use to award posts/comments. The bigger awards (e.g. gold) grant the recipient a week of reddit premium features and some coins they can spend themselves.

Most people probably aren't paying for the "reddit coins" per se, they're paying for the other features. Then they spend the coins to award comments and posts that they particularly like.

The fact that "coins" cost money and are limited means people tend to think more about what they spend them on, so the awards are a lot more indicative of what people consider to be valuable content than free up/down votes.

They aren't getting rid of the paid reddit premium subscriptions, they're just getting rid of the current system of "coins" and awards. They say they plan to replace it with something, but there's no indication of what the replacement might be.