The Sims 4 actually has heaps of NPC's, it's just weird they overlooked the major ones:
Maids
Pizza
Mailmen
Gardener (there are actually two types. One will be around community gardens watering, the other type clean up parks)
Librarian (they put books back when Sims leave them around, and basically keep the library looking nice)
Mixologist/Bartender
Entertainer
Fitness Trainer
Curator
BONUS: There is actually a Repairman in the game, but you have to use a cheat.
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Ranger
Bear
Hermit
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Aliens
Police (I have seen one or two police walking around Magnolia Promenade near the Pier and Gardens near the chess tables).
Doctor (They will also walk around, occasionally. I had a Doctor check for fever on my Sim, when I was trying to get with him x)
Still hoping for Fireman (despite Sprinklers actually being better, mainly for ambience), Burglars and Butlers soon :)