The novelty of tech is pretty inconsistent in Trek. At the beginning of TNG holodecks are treated like special new technology, with characters walking in amazed at what they're experiencing during the first two seasons. But then by DS9 holo tech is treated as if common place. Then in VOY Janeway reminisces about her adventures in the holodeck as a child, over the same program Naomi plays in.
So with all that and TAS in mind, TNG's earlier episodes are kind of an outlier with holo tech being a novelty. It was likely treated as such in 1987 as if to retcon what was seen in TAS, as the rights were out of Paramount's hands at the time. Now it's all canon again.
That's not really accurate, though it's an understandably common misconception. It's
not portrayed as a wholly new concept to the characters. What is portrayed as novel to them is how
indistinguishable it is from reality, the level of tactile and sensory detail, the lifelike characters that can be conversed with and respond spontaneously, etc. No one actually spoke or acted as if they had never experienced
any sort of holographic simulation before, just as if they hadn't experienced ones
this good.
"Encounter At Farpoint" (TNG):
DATA: This woodland pattern is quite popular, Sir. Perhaps because it duplicates Earth so well. Coming here almost makes me feel human myself.
RIKER: I didn't believe these simulations could be this real.
DATA: Much of it is
real, Sir. If the transporters can convert our bodies to an energy beam, then back to the original pattern again...
RIKER: Yes, of course. And these rocks and vegetation have much simpler patterns.
DATA: Correct, Sir. The rear wall...
RIKER: I can't see it.
DATA: We're right next to it. [throws rock right over Riker's shoulder to reveal wall]
RIKER: Incredible!
WESLEY: Commander Riker! Commander Riker, isn't this great? This is one of the simple patterns. They've got thousands more. Some you just can't believe...
RIKER: Careful, the next rock is loose!
(Then Wesley falls into the water and
really gets wet, and
stays that way upon exiting, tracking it out to form a puddle
in the corridor. It's not just holographic, it's
real, and it persists
outside the room!)
"The Big Goodbye" (TNG):
TROI: You could be over-preparing. You've been looking forward to the upgrade of the Holodeck. You have the time. Captain, you need the diversion.
[...]
PICARD: From that window, I could see an entire...
DATA: City block.
PICARD: That's right. Sounds! Smells!
CRUSHER: You make it sound so real.
PICARD: Well, that's how it felt!
[...]
PICARD: The sense of reality was absolutely incredible! When that woman kissed me, it was so...
CRUSHER: Exciting?
PICARD: Real!
(Troi even refers to it straight out of the gate as an
upgrade, meaning it's
not an entirely new thing, just an improvement on something that came before.)
As the quote from
The Making Of Star Trek I posted above shows, Roddenberry had conceived of something akin to this at least as far back as the second season of TOS, and actually planned to show it in the third. It just didn't come to fruition thanks to a combination of budgetary restrictions, his stepping down as line producer for the third season, and ultimately cancellation. But as we can see from the animated show, this was still in his mind something that existed aboard Kirk's ship. As with so much of TNG, his idea there was to present a new-and-improved version that would blow away—perhaps literally, if you're not careful—even those who were experienced of older models.
And it's not hard to make sense of Harry's comment from "Flashback" (VGR) about there being "no Holodecks" (nor "replicators" as opposed to "food synthesizers" or "protein resequencers") on starships in Kirk's time, either. Once all the evidence is taken into account, it's fairly inferrable that a "Holodeck" specifically is a highly-developed combined facility incorporating the utilitarian purposes of holographic combat simulators as seen in DSC (following on from the very rudimentary holographic target practice systems seen on ENT in episodes such as "Sleeping Dogs" and "Harbinger")
and the recreational purposes of the facility from TAS, and expanding on them both, being also useful for scientific research, engineering simulations, and any number of other uses. (It's like a department store or a shopping mall. Before there were such things, there were still stores and shops of all sorts. You just couldn't necessarily find them all in one place.)
This is even further backed up by the fact that the holosuites on DS9 never get referred to as proper holodecks and are even distinguished from such in "Take Me Out To The Holosuite":
SOLOK: I need use of a holosuite. The T'Kumbra
holodecks are currently under repair.
SISKO: To arrange holosuite time you have to go through Quark. He owns the only ones on the station.
(I know we had a whole other
thread on this subject already; sorry for the repetition. It's worth repeating, though.)
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MMoM