Also, Nynorsk really is a minority (spoken by only about half a million people), which makes it harder to create a corpus for automatic translation.
If I remember correctly from Norwegian classes growing up, Bokmål is heavily influenced by written Danish. Nynorsk was based on dialects people spoke outside of the bigger cities. Nynorsk however is more of an amalgamation of dialects, and can not be said to be spoken by anyone. Your estimation is in the neighborhood of native writers of Nynorsk I believe.
Also, in television and radio, you may hear people trying to speak nynorsk pretty much as it is written, especially if their personal dialect is much closer to bokmål. (So-called “NRK-nynorsk” :-) )
Since the majority speak some dialect of bokmål, and most courses teach it, that's what you end up with.
I watch some series in Norwegian, e.g. Ragnarok. I understood most of it, though some of the dialects were kinda hard to understand.
But it seems a moot point, basically nobody in any language speaks the "high" language, but some kind of dialect version of it.
When teaching Norwegian to foreigners there's really only one practical way of doing that - use an artificial "spoken" bokmål so that the students can actually match speech to written words. That's just a crutch in order to learn the language (after you're done the real learning starts). That doesn't mean that "spoken" bokmål (or nynorsk for that matter) is real outside the learning institution.
English, say, also has many spoken forms but more or less one written form.
If you learn written English and then move to the Highlands or Australia you are also in for some heavy learning.
Probably they had that one Norwegian employee who struggled with it in school and came to hate it as a result (you'll find plenty of them in this thread).