Some developers like to establish a relationship directly with their users, not pay (in dollars, or advertising) a middle-man like GitHub, GitLab, or an App Store.
But look at it from the other point of view: how does a non-technical user determine if a binary download is malicious?
And how, then, does Google/Microsoft/Apple protect those users from their ignorance?
Given that the internet is full of people attempting to get non-technical users to download malicious software, often my mimicking exactly the sort of site the OP has created, then is it really practical to insist that Google/Microsoft/Apple allow the OP's site to download software to a user's machine freely?
The advantage of the middle-man is that it acts as a trust agent (not necessarily well, of course). If you download a malicious binary from an App Store, that is the App Store's fault for letting it on there in the first place.
Let's say I keep bees as a hobby, and I write some small piece of software that tracks and calculates something to do with honey production. I post it to my favourite bee-keeping forum, other people try it and like it, and when a new bee-keeper joins the forum they're often advised by forum regulars to try my software out too.
That kind of software can be a huge help to people, but it's not a good fit for an appstore because it's never going to turn a profit, and at least on Apple's store (with the $99/year publishing fee) it'll drain money quite predictably and regularly.
A bee-keeping forum will never be trusted by as many people as Google/Microsoft/Apple, but the people who do trust it probably trust it a lot more.
With that said, hosting the binary on those platforms won't necessarily help as Google can flag individual repos according to some other comments here.
I would, if at all possible, prefer to find a solution to this problem so that I can directly host my software.
At some point your domain will have a sufficient score and it will not show the warnings to users.
How long that will take is, however, outside of my knowledge and it would be nice to have some official reference about it; as it stands I agree with you that it feels like begging to a benevolent dictator.