I was a delighted paying customer of OmniGraffle for a decade, and looked forward to each update.

I also payed for multiple version on iPad.

However at about the point that they released their own sync service, they just let it stagnate.

There are so many ways the iOS and MacVersions could be more modern and more useful on a day to day level, none of which require a massive re-engineering effort.

My conclusion is that they have just fallen behind the times.