I'm not seeing the problem of offering a discount to new customers. The new customer is taking a risk by accepting a new vendor, and hence to entice them the vendor offers a discount.

Now, if the vendor continuously offers the discount to the customer just because they keep asking for it, then that is unfortunate. But I usually only see this with monopolies, like Comcast. I'm sure their strategy is to do that on purpose just to satiate the vocal minority.

The problem is that it removes any incentive for loyalty and encourages churn, while being a pain in the ass for the customer. What benefit can possibly come from getting people to constantly switch providers?

That would be a problem for discounting for people who threaten to cancel or cancel and re-subscribce.

That is not a problem for new customers, who have 1 chance to try a new product.

In this case, "new customer" is anyone not currently subscribed. So if you go from provider A to B and then back to A a few months later, you're a new subscriber.