They can be, sure, but they can also be a really good deal. If I know I'll need a certain amount of something on a fixed schedule, I can subscribe to it and save money. This helps reduce costs for suppliers because they have a better idea of how much stock they need on hand, so they'll want to encourage you to subscribe with discounts.

Subscriptions are bad when there's some form of lock-in, such as a fee for breaking the subscription, or if the cost is arbitrarily high without the subscription because of a lack of competition. I dislike digital subscriptions in general because of this, since you'll lose access to all of the content you've enjoyed to that point.

But subscriptions to consumables are fine by me.