Last week Bank of America and Chase announced they are killing their Windows Phone native applications. The reason stated is lack of use. Does this mean Windows Phone is dead? No, over 10 million Lumias alone sold last quarter. The reality is supporting multiple independent native applications across multiple platforms is expensive. Right now there are 2 main players in the 'mobile space', iPhone and Android. Windows Phone is a distant 3rd, but that really does not matter?
Creating a modern client application is expensive, especially if you need to support the potential scale these two banks posses. Each of these banks are major US players and offer products across a broad range of banking needs, car loans, checking, savings, mortgages, etc. Both have millions of potential customers using their applications. Hopefully each platform's client application accesses the same API as the other platforms, but there is not guarantee. If not that also compounds the support overhead.
The harsh reality is the vast majority of 'apps' simply cannot sustain themselves. Most app developers and companies operate well below the app poverty line, or simply put loose money. While mobile banking is a great feature, and every bank should offer some form of access. Like any product or service a bank or any other company offers it costs money to offer and operate. The decision to cut these Windows Phone applications speaks more to the cost to service the applications than it does Windows Phone popularity.
The majority of non-gaming applications on mobile platforms rarely utilize the pure native API features on a platform. Full disclosure, I never used either of these two banking applications, but have used a few other native banking applications. Mobile banking applications are all pretty much the same as far as functionality; check balances, transfer funds, deposit checks and possibly pay a bill. Nothing there really screams native application because all these features can be accomplished using standard web technologies, including uploading check images.
At this point I have several years of experience building modern web applications that allow end users cross-platform access. A banking client like the Chase and Bank of America application's could be done in under a month give or take 6 months depending on the level of excessive enterprise overhead. The biggest obstacle is defining what level of Android support you are going to tolerate. I am also making the assumption the API is developed and you have a good graphic designer to create any potential assets. Multi-lingual support is also a potential aggravating factor. But even with aggravating factors a mobile banking web client should not require a lot of engineering.
The common banking application, like Chase and Bank of America, represent strong candidates for a rich cross-platform, responsive, single page web application instead of numerous native platform application. Development and support costs are far less than native counterparts. The real costs associated with any client application are customer support and maintenance. Banks like Chase and Bank of America most likely have a minimum service level agreement for customer support staffing. This overhead, combined with lack a smaller user base certainly hurt these two applications. Having a single web client experience means these two mobile banking experiences would be available on Windows Phone as well as an other client platform the customer chooses and at a lower total cost of ownership.