Big Tech also formed a cartel to lower engineers salaries. This is also something that should be punished by law (and AFAIK, they did win a class action suit).
I do think this is a problem and needs to be addressed.
You might see antitrust law force Apple to allow sideloading, including apps built by toolchains third parties have hacked together.
You're also not required to use a Macbook; the Mini is $500.
If a monopoly is allowed to choose, it can use its domination in one vertical to influence another vertical.
Anyway, I would prefer a Linux version of the iPhone SDK. I do not use neither Windows nor OSX normally.
If you don't like the MacBook, you can buy a Mac mini and use it as a build server from other (non-Macintosh!) computers. There are tools for other platforms, and Apple isn't obligated to maintain their platform for "non-standard" use. It's not antitrust, and it's not a technicality. They're not obligated to open their platform, because they're not restricting something that was previously open.
I don't like it either. That doesn't mean it's illegal.
They are Big. It's a word that describes how they can shape policy and public opinion in a way that smaller businesses can not, and that competitors' interests are aligned enough that they routinely collude via lobbying organizations or other means (Big Tech is catching up in this area).
My opinion is that antitrust laws and such are not applicable here because even though the companies in question have an effective monopoly on traffic, it does not make it impossible for other players to create a profitable business.
Google is not a domineering empire like Standard Oil or Ma Bell once were. They do not have total control over everything. Even if they have a certain product (for example, Google Drawings), it doesn't stop other smaller players from making quality products that people buy (Sketch, Illustrator, Inkscape, etc.)
I don't really think this is a problem. (And where it is, existing antitrust laws are performing as they should.)