Is it really that hard to understand why people wouldn't like the idea of using EGS? Yes, it meets the bare minimum of functionality for a launcher-storefront. AOL also meets the bare minimum of functionality for an ISP. Huawei meets the bare minimum of functionality for smartphones. There are still massive downsides to trusting these companies with your money and data. You can't expect most customers to be fine with the bare minimum, particularly when the competition has been providing far more than that for years or even decades.
I can understand a minor distaste at a minor inconvenience -- if they made it to the point in life where they can sign up for a crowdfunding effort they can surely make a throwaway for a one off game. The level I am seeing here (one bordering on or showing some of the hallmarks of various computing holy wars or console wars if we are looking more at games) is not one I can understand. It is not like the backers are not going to get the game, or not going to get a major component of the game. It is not like Valve/Steam are some innocent little entity so benevolent in nature that risking their happiness is an affront to all that is good in the world, or that Valve/Steam is holding back the tide or keeping things funded/ticking where others would not*.
*I know they are a decent contributor to a lot of open source, and the long term is nice but by the same logic Epic is funding sure to be popular, artistically or culturally relevant titles and surely that also counts in this equation.
I necessarily don't expect customers to be fine with the bare minimum (though I am still dubious on the value of sum total of valve's token offerings -- maybe it is that old Microsoft word thing of everybody uses only 10%, but a different 10%), though history has shown they can handle it a lot of the time. From what I have seen I would similarly not call it bare minimum, or at least it is not the latest in a long line of abusers or the term alpha or beta.
Similarly I have generally found Huawei to be a reasonable maker of phones -- if nothing else they still offer external cards and a 3.5mm jack, all with half nice hardware, which is more than can be said for a lot of things these days. Bit light on the easily swappable battery but baby steps and all that.
Because its the Epic Games Store and they promised the backers Steam Keys upon launch but since its gonna be an EGS exclusive that's not possible. The EGS is a failure you have to admit.
I don't know how we can call EGS a failure if it is still actively supported and developed -- I am sure they would have loved Valve, GOG, gamersgate, greenmangaming, whatever Discord are doing, humble bundle and all the others to get on the blower and say we are chucking in the towel, here are the keys to the front door. It might well end up a failure in the future, no great loss though if so.
As for the first part are Steam keys such a valuable part of the game that you would refund investors? I get it for multiplayer that will never come, or single player that will never come, or some minigame/boss rush/similar extras that might never come or something of that sort of magnitude but again something that will run on the same hardware, the same OS, no radical software tweaks needed, be the same game it would have otherwise been (if not better), at presumably the same launch timeframe, require no subscription... why the fuss? If Valve had decided to stick up the middle digit to the devs here (we will go with for no good reason, mainly as Valve have done that in the past) and they had to find a home on GOG or something instead would there have been the backlash?
Because, regardless of your thoughts on steam or the epic store, it's a change in the terms made after the money was already paid.
It is a change, one I would argue is quite minor, in development goals after an investment was made. Not really the same as a hard contract, or a major claim being unable to be met.