We did have an iPhone app initially, but we scrapped it.
We found that trying to get clients to install a custom app was way more hassle than just sending them to a webpage using a browser, which is already on every phone.
If you're doing a demo to a client, or want to show some content to somebody on the spot, getting them to download an app first is a pain. Depending on data plans and download limits, they may not even be able to download a larger sized app unless they're on WiFi!
A large percentage of people will simply move on if they’re forced to install an app to do or view something. One less step in getting your content to them means lots more engagement for you.
Another reason is that people with strict corporate plan phones aren’t actually able to install new apps, but they already have a browser, so there's another potential segment that you miss out on.
A really big reason: everyone always gets the latest updates and features instantly, on any phone/desktop, without having to keep apps updated.