Because a relationship between two middle-aged adults wouldn't do much for the ratings, but any scene with Seven -- especially a romantic one -- would.
After re-watching it, knowing what happened during ENT, this is the logical explanation for all the Seven-centric stuff they put in VOY.
To be fair, there is also a large number of fans who are happy J/C did not
I'm in that camp, though I'd prefer not having any C/7 stuff pushed down my throat either. It was quite obvious that they regarded each other as more than friends and I can't be alone in noticing that she drifted away from leaning at Tuvok for support to Chakotay and the warmth that grew between them. Janeway makes it clear though several times during the series that she can't indulge in a relationship. Her obligations is to the crew and getting them home.
I liked it the way it was developed during the first seasons because it left a lot to imagination. It wasn't intrusive either. They were grown ups with a lot of responsibility and had their priorities straight. Good enough for me.
The Seven thing? Ugh. Not believable at all.