I'm attempting to do this in my DMSGUILD products going forward, it dramatically increases the size of the statblock (even cutting out the non-combat spells).
There are ways to mitigate the stat block bloat caused by in-line spell description, but they all require a compromise of one kind of another that deviates from what's being done in official products.
1. In an adventure heavy with spellcasters, you can have a curated "Spell Brief Index" which can be printed separately and referenced whenever one of those spellcasting NPCs/monsters uses a spell. For example, I've used this approach for an adventure filled with fire mages.
2. You can reduce the number of spells known and heavily shorten/annotate each spell description. However, in published products this may necessitate an introductory bit about "Reading Shorthand Spell Descriptions." This is my baseline when transposing spellcasting monsters for my home games; for example, I did this with Acererak's spell list in Tomb of Annihilation.
3. You can overhaul the design of spellcasting monsters in 4e style, focusing on 3-5 unique magic effects that drive home that NPC or monster's identity/theme. These can include certain spells, such as
mirror image, written in shorthand. But they can also include merged effects, such as combining
stinking cloud and
darkness or
arms of hadar to get "Darkening Cloud", then putting it on a recharge timer. The key with these is to denote them as spells with levels, for the purposes of being
counterspelled (if that's important to you). For example, I just did this – in a very rough form – for an "enchantress" NPC in the game I'm running for my nephew.
I don't think any one of these is the perfect solution, but in my experience any of these 3 approaches is superior to the way the 5e Monster Manual is written in terms of ease-of-use and accessibility at the table. Flipping through the PHB or even DNDBeyond (when juggling multiple files/windows and internet lags) to find the right spell, then having to do it each round or multiple times a round, kind of sucks.