I understand the importance of preservation for historians, hardcore fans, etc. but the pool of customers who are interested in actually buying the OG versions of H1 and H2 are probably not that big. I can't imagine a for-profit company having much impetus for doing this, especially while they're pouring more money into the MCC, but who knows. Yes, H3 got the treatment but I'm pretty sure I read they used it as a test-bed for the BC technology so it was kind of a freebie. Also, there is a huge difference between H3 and OG H2, which is the servers and matchmaking still work with H3. Making H1/H2 BC may not be that difficult, but releasing them for BC with no matchmaking support seems like a recipe for complaints and disappointment. If you add in the cost of developing some sort of matchmaking solution for them, it then certainly becomes a money-losing venture.
After saying all that, I think they'll probably release them anyway due to Halo being one of their core IPs, but it will probably be sans matchmaking on H2, and there will be lots of complaints.