Strange that it doesn't look as good as Blu-Ray TOS even though both were filmed in 35mm film. The Blu-Ray "Enterprise" still looks really good
It's not that surprising, Enteprise is using decade old masters created for HDTV, techniques have come along way in the last ten years just look at the Gladiator Blu-ray, the first release used an old HD master created for the 2001 DVD release but it was awful so they did a brand new transfer and it looks fantastic.
Enterprise could look as good as TNG if they rescanned the negatives and re-rendered the CG but that isn't going to happen, like you said it looks really good so why spend a lot of money to make it better when most will already be happy with how it looks now.
Yes, plus they can re-release it in a couple of years in better quality so we will have to buy it again, lol.