WP is attracting the type of customers that aren't valuable in India and Australia - those that are only looking to buy the cheapest device possible. Windows Phone isn't doomed because it's selling too little. Windows Phone is doomed because the bulk of Microsoft's customers are only buying solely on price, and commodity manufacturers like Micromax are going to snuff them out. Quite frankly, the transition that's happening that is WP's "growth" is end users that are ditching the bottom tier BlackBerry phones for the cheap, sub-$130 dual sim WP devices.
Not all consumers are equivalent. Market share as your sole metric is a failure unless your product is a commodity, single-use object (e.g. traditional CPG like Kleenex). Stickiness is important with smartphones when device turnover is high.
Re: Xiaomi
Xiaomi doesn't need to bring their phones to the United States to be successful. It's a very western-centric mindset to think that's an inevitability. Sure, we have the world's best consumers in terms of buying power, but they're already selling to the world's fastest growing middle-class, and they're creating a suite of hardware that ranges from speakers to air purifiers. Xiaomi's more than a phone company. They're a full stack home products company.
They don't need the hassle of entering a brand new market where they have limited ability to take advantage of their direct to consumer knowhow and the extremely high costs of doing business here.