> Epic pays for temporary exclusivity
In several cases, they sought out games that were already coming out on Steam and even had preorders (or kickstarter backers) there, and then paid those developers to rip it out.
There is a seemingly minor but important distinction with what Epic does: they do not pay for exclusivity nor do most of their actions involve paying for a game to be made that otherwise would not have been. Either of those things are fine, even if begrudgingly.
What Epic actually does is pay to harm Steam specifically; the stipulation is always "don't put it on Steam", not "only put it on our platform". It is purposely targeted and antagonistic towards steam and steam users; "we have deprived you of a thing, now you have to come here if you want to get it" is how that comes across, when they should have aimed for "we are getting this new thing made for our platform, come over here to check it out!"
While they were doing this, their store was in a miserable state compared to its competitors, in terms of features and reliability (especially for the desktop app). So they were seen as prioritizing depriving another platform instead of prioritizing having a good platform and customer experience.
When all of the above is put together, it comes across as petty and malicious, rather than them trying to throw their fortnite dollars at bootstrapping their platform, and at making and having a quality platform for consumers.
If they had simply paid for a bunch of new exclusive games and IP to be made for their platform rather than seeking out existing, already advertised and in-development suitor games, it would have come across way differently. Or if so much more of the effort and money would have gone to making the store better and beyond feature parity with its main competitors (not that it necessarily reached even that), it would have been received quite differently.