I'm just as confused as you are as to why anyone on the planet would click where the "attach image" button used to be, see a popup for gifting Nitro, and go "sure, let's do that instead", but evidently Discord thinks that at least some people are going to do that, or else they wouldn't have made such an absurdly hostile change in the first place.

Presumably they're banking on people who would have gifted Nitro in the first place but were just unaware of the feature.