Some quick math suggests that Jepp have just kissed goodbye to $10-20M of
business/year. What are they thinking?

They were thinking that the business they would lose by doing this would be
far less than the cost of buying back all those unused retail kits every
month, a condition demanded by more and more retailers. They were thinking
that they could reduce an enormous GA liability problem, seeing that
airplanes piloted by professional pilots have a much better safety record
than airplanes piloted by, well, unprofessional pilots. They were thinking
that most pilot shops refused to carry their products anyway. They were
thinking that their electronic chart business is expanding at the expense of
their paper chart business. They were thinking that by making people
subscribe they are reducing the chance of an accident caused by cheapskates
who don't keep their charts current. They were thinking that they could
actually reduce overall distribution costs. They were thinking that they
could cut out the middleman in an already low margin business.

How do you know all this inside thinking by the folks at Jeppesen?