Simple, because the app is sold (distributed) by different companies. And they don’t cross market.
JyotishTools Pro came about for two reasons: 1) that more users wanted to do mobile what they were doing on desktop or laptops and 2) for an Android market that wanted a layout for JyotishTools on their 7” tablets like was available for 10” Android tablets. As it turns out answer 1 anticipated a trend that is actually occurring in the tech industry. More people are doing what they were previously on desktop on mobile.
But I get a lot of emails asking if they buy JyotishTools Pro on Android or even iOS can they also have JyotishTools Pro bundled for Windows. Nope, not possible because you won’t get Microsoft, Google or Apple cooperating with each other to make it possible. I doubt if it will ever happen. In fact it is currently not even possible to bundle an iOS app and a Mac app on Apple’s AppStore.
As for answer 2 unfortunately the market for the landscape layout that JyotishTools Pro for Android tablets did not materialize. I do have an alternate layout that could lend itself to having one Android and one iOS app for both phones and tablets. The problem is that many users get used to an interface and an changing it dramatically even though all the same functions will make some users upset.
Small factoid here, actually the “classic” JyotishTools for Windows began as JyotishTools for the PocketPC. It was possible to take that PocketPC code and implement it for desktop Windows since the PocketPC used a subset of the Windwos operating system.