Because it's not for the developers I know – they either want a Macbook or an infinitely configurable (hardware and software) workstation, whereas this has the configurability of a Macbook with the ease of use of the workstation, clearly not a combination people want.
I can only assume this is for mechanical keyboard collectors. Developer-adjacent tech enthusiasts who like the idea of Linux, without an actual professional need for it. People who like well built devices, but don't really care about swapping out hardware. People who have a lot of disposable income and want to buy cool things.
If that's the target market, that's fine. I guess the problem is that market only buys it if you claim its for a different market, developers/etc. As a result it's going to rile up developers every time as they always feel the need to push back with "this isn't what I want".