Ha!!
This is likely the most accurate answer. Hence the middle management-calinber "we're too busy" response.
Reading the posts of others in this thread is why i made such a comment. Other posters have commented on the fact that there are some very good ipad apps that have been developed by either a single person or a team of two. There is also that fact that Instagram is not only a platform for posting ones pictures on but also for others to comment on and where are a huge majority of these comments going to be coming from? yep, you guessed it, people sitting at home on their sofas/couches with their ipad.
It would be extremely easy for Instagram to hire a 3rd party app developer who could develop an ipad app in a number of days, even a week, which is how a lot of companies get their apps developed, by hiring specialist ipad app developers BUT the only way social media companies like Insagram can make money is by targeted ads OR harvesting customer data and selling it on to 3rd party advertisers or 'associated partners'.
When you install Instagram on the phone, it comes up with a message saying 'this app would like to have access to your phone camera, your contacts, your location, do you accept? If you do, this means some of your personal data is sent to Instagram which they then sell to their 'associated partners' (many apps and websites are doing this). The large majority of ipad owners do not have phone capabilities so asking for such information is pointless, hence Instagram not being able to profit from ipad users.
Like I said before, once Instagram has figured out a way to harvest ipad owners personal details, then you will see an app developed for it.