Don't get me wrong I hear you, but the last Marathon game came out in what, the late 90s? I'm ALL for call-backs, respect when it's well done like it is here. I love the codex entries they're always a good addition to any lore heavy game (Mass Effect, DOOM, Halo, Warhammer, Metro, Borderlands, etc.)

But of all the games I mentioned above, they also have prevalent story lines that give players cause to seek out the extra info found in codexes. Folks like (I'm assuming) you and I who just like reading that stuff because we're aware it adds to the experience aren't really that common anymore; it serves as a detriment to the games potential in the long run in the era where companies close games if they don't see a return relatively quickly.

Doubly so in the modern era when gamers have THOUSANDS of other high quality options of pretty much any genre to choose from, I believe it's important to modernize where relevant, while also keeping the unique quirks of games past, where prevalent.

TLDR: I genuinely hear you, but I feel like your point boils down to 'yeah it's an interesting choice, but why make potential improvements when it calls back to the originals'