Well, they need someone to tell them.
I disagree. Because I do not think in this day and age we can assume new players are that stupid.
First of all... I do not think most new players are going to have nearly the same sort of issues with "NPCs look like PCs" that so many of our veteran players here are so annoyed about. THEY want the 5E24 MM to have different things because apparently they don't want to bother spending their time making the game "work" in the manner they want. They seem to prefer the game to just be "plug and play".
New players? I do not believe they will ever see this issue the same way as all the veteran players here, because that only really comes from actually playing games that had things differently and then being able to compare-and-contrast. IE: 5E14 had NPC spellcasters with full spell lists, 5E24 does not-- and if I want my players to be able to pick up that spellcaster's spellbook I now have to go through the effort of "creating" one myself. I'm now "worse off" using 5E24 than I was using 5E14.
But new players have never experienced 5E14! So they have no idea how much "worse off" they are, nor do they probably even think that this sort of thing is an issue because they are learning the game this new way that doesn't take the PCs gathering the enemy's spellbook as a normal thing to do. So there's nothing gained or lost for new players, because their games are so much different than the veteran players here.
Unfortunately though... this is something we get a whole lot of people here on these boards always doing... which is
speaking on behalf of the "poor newbs" out there who are not getting something they "obviously need" because the speaker is the one who actually wants it it and thus if
they need it then of course new players need it too! Like the 5E24 DMG "telling new players they can use outside sources from the three core books if there are things they want to have in their game that the three core books do not provide" as though they couldn't possibly come up with that idea themselves.
The irony of course is that in this particular case... it is veterans who
do not need to be told something still wanting that information made available in the books for other players for... reasons. They will SAY it's because they are trying to look out for the little guys... but if I had to make a "wild assumption", it's because those veteran players can't stand the thought of Wizards of the Coast possibly producing a game that doesn't match their expectations of what a proper Dungeons & Dragons game should be. It's as though the owners of D&D are tacitly telling us that how we run our games is
wrong. Now I don't believe that's in fact true... but it's the impression I get from a lot of people here on EN World. But I for one do not have my ego so fused to this game that I give a rat's ass how WotC or anyone feels about how I run my game. So there's zero need for any of these books to ever match my expectations or desires. It's too bad more people don't feel the same way, because I think they'd all be a lot happier.