A lot of people in the US switch to Android for reasons unrelated to what you think the benefits of Android are. My guess is you don't think Android's biggest draw is bigger screens but a lot of people in the US switch because of that.
Actually it's the biggest negative of Apple and all other manufacturers are better at reaching peoples' requirements in this case. I bet Apple will release bigger screened Iphone this year though due to this, just because of how ridiculous the size difference has gotten between the Iphones and all other major flagships (Android, WP). Now I know there's a minority of people who want smaller phones. There are many other "minorities", such as the power users - due to the fact that most phones are becoming similar these days those minorities are getting neglected in favor of aiming at the few most popular user groups. I find that Samsung and Apple are trying to be the most versatile, while both omit some groups - Apple omits the power users, while Samsung omits the users who actually want a really premium feeling device.
We have Samsung's R&D here in Poland that is responsible for making software for Samsung phones, including preinstalling bloatware for each market separately and "gimmicky" features.
Most of bloatware is preinstalled because Samsung signs contracts with third party software makers in order to deliver the most popular apps preinstalled because they assume most people are not going to download apps.
Most Android makers install them so people don't act like "oh my phone doesn't have Facebook/Dropbox/TripAdvisor!" just because it's not preinstalled.
"Gimmicks" are a separate thing - they are in fact included in the custom launcher (Touchwiz, Sense) and deeply rooted in phone's software and only they are understood (by OEMs) as means for differentiating from other manufacturers.
iOS has less gimmicky features and is less bloated with apps partially because it's more basic out of the box and doesn't feature Google services preinstalled, unlike Android, so it feels less overwhelming - but you're going to end up installing most of the apps that are preinstalled in Android anyway.
There are also no widgets, it's harder to fill the launcher with "gimmicks" because of that OS being aimed at less tech savvy users, not power users whatsoever. Siri, iCloud etc. are Apple's "gimmicks" though.
I know that the American market and choices made in the US are different compared to other countries as well. The preferred size and price range of phones is different and features that people want are different. Most of all - outside of the US, Android unit sales are driven by low to mid-end devices, which alone makes the market situation entirely different.
In China people buy phones that look more "fancy" by the Chinese standards which are entirely different than American standards, and it's a potentially bigger market (as far as we're talking about units sold). The awareness of amounts of CPU cores (even if they're shitty) and dual sim are very important as well - things that people don't care about in the US.
In South America and Africa people buy smaller phones so mini variants dominate the markets etc.
And the US is not the biggest market for Android - it's just the biggest market for Apple.
Also in general Android phones in the US (especially those that come from certain carriers) are bloated significantly more than their global variants.