Well, Nuance not only have a huge foothold in the education industry, but also in the government/healthcare industry. They're very deeply rooted in a lot of things and they've had a lot of legacy issues that caused outcry. For instance, when Lion (or was it ML?) came out, they didn't have a compatible version of Dragon Dictate. They said they'd update it for the latest version, so thousands of copies were bought in the thought that it would soon be patched for compatibility.
Nuance responded by bringing out a new version of Dragon, Dragon 3, that would be paid only. Didn't patch the old version. ****ed a load of people who sunk £150+ into software they didn't do jack with.
Stuff like that is the tip of the iceberg. Too many fingers in too many pies, and too many mistakes from too much greed. Buying them outright is too much trouble.