When x is standard workflow for many of the other such programs (and things like word processors) and it isn't such in Gimp, that very thing drives people away. Most artists aren't going to care what the software engineers want in the program: Instead, they are going to care about things like this. When added up, it just makes for a frustrating experience. It doesn't really matter what the technicalities are if you are the artist.

Yes, you do lose some information depending on the format. Heck, I notice loss simply looking at an image on different screens. The fact is, though, that folks actually need to save in different formats. Sure, I keep my layers and information in tact while working, but folks also need to be able to share their work, print it, and things like that. For that sort of thing, you need the different formats. The exact format depends on what one is doing: PNG works for facebook and instagram. Some sites have file size limits, and with some printing you have a bit more leeway.

I'm not even a photoshop fan myself: I chose my software based on both if it was easily integrated with a Wacom pen display and how well it mimicked traditional artwork flow and styles. Hence my use of Corel. Photoshop is basically a renting program now, and I generally welcome alternatives. Gimp has always been somewhat frustrating because of little stuff like this.

As a user, I think about "saving" as a process to persist my work. If there might be technical fine-grained issues, show me a warning sign in the save dialog, but don't come up with a process that "makes me think".