OK, I just figured it out. You are a niche company that makes a good product and you get good sales, the problem is you don't get enough sales to make enough profit to keep the shareholders happy.
Then the OSes you support get changed so much that you have to develop the new versions on them, but the programming language you use got changed to support that new operating system, etc. So you have to pay for training your developers or hire new developers to work with this new technology.
IBM had this problem with the Lotus series and Windows 9X. The Windows API had been changed so much that it broke Lotus Smart Suite and the cost of rewriting it to work with modern Windows like Windows 2000/XP had cost so much that IBM had to fork OpenOffice.Org into Lotus Symphony which was easier than rewriting Smart Suite and cost a lot less money. But it failed. Also, that darn DOCX format broke the Lotus products trying to be compatible with the old and new office file formats.
So this is a problem that the so called Unicorns that do just one thing great have to face.
I wonder why more isn't written about it? You can learn more from a failure than a success.