Are you sure they only look at syndication revenues? From what I heard Season 1 of TNG in HD made its money back just from blu ray sales in the first few months. Also there is the money they make from people watching online through Netflix etc. Who sits down in front of broadcast TV these days anyway? The elderly thats who and they wouldn't watch Star Trek even if they were payed to do so. Therefore, I'm sure they take all types of possible revenue into account. I'm also sure they look ahead and have thought about how they will be selling this stuff in 5-10 years. Online watching will play an even greater role then.
Syndication is not the only source of revenue for the remastered episodes, but it is by far the biggest and most important. Home video has been continuously shrinking for at least five years. Obviously it is still a revenue source (the bonus features wouldn't exist, otherwise), but compared to syndication it is less important.
Streaming is growing in importance, but syndication is still more important (especially globally).