There are valid arguments both for building fully native mobile applications as there are building cross-platform applications.

The argument for the latter generally falls down to cost, time to deliver, and resource (programmer) availability.

Working on one code base targetting multiple platforms seems to be an obvious choice. However there are some often overlooked caveats.

With the single code base approach, it's possible to have one resource building an app for multiple platforms.

Developing natively cross-platform generally requires at least one resource per platform.

That obviously incurs additional cost and planning overhead, but in the long run, it can actually be beneficial.

The single resource approach asks one resource to be overtly familiar with all platforms they're targetting. They must know the nuances of the entire process of provisioning an application to get it live on its relevant distribution platform (or app store).

That's a lot to ask of one resource.

In addition to this, the resource working on the app is likely to be anecdotally more familiar with one platform than another, designers are going to design "one" app disregarding the different ways users interact with their platform of choice. There's a level of expectation on how something should look and work on a particular platform that may differ from another. All this is harder (albeit not impossible) to manage with a single code base.

There are clear and valid reasons to build cross-platform apps, but there is still place for fully native applications in our current environment.