Exactly....
Theaters use 32, or even 64, speakers because they're trying to provide a consistent, or at least decent, experience for everyone in every seat.
(And that includes seats right in the middle as well as seats located directly under the furthest corner surround.)
If you have a small room, and you're sitting in the prime listening chair, then something like a 5.1.4 system will deliver pretty much the best experience you're going to get.
Even with a larger room, if the room is good, and you're going to stay parked in that chair, you're not going to gain much by adding more channels.
The benefits accrue if you plan to move around, or have multiple people sitting in multiple locations, and especially if some of them are far from that prime position.
It's also worth noting that, in that situation, there are limitations in what you can achieve, no matter how many speakers you have.
For example, if you have one seat that's way over on the side, right in front of a surround, the sound from that surround is going to drown out most of the other stuff for the person sitting there.
And there's no real way for you to fix that beyond lowering the level of that surround so far that it's inaudible to everyone else.
In real life everyone doesn't actually get the same, or an equally pleasant, experience.
If you're the guy standing next to the car that's revving its engine you're not going to be able to make out what the guy standing fifty feet away is saying...
And, if you were really standing twenty feet away when a real grenade went off, you wouldn't hear anything anybody else on that battlefield said for quite a long time.
We leave it to the sound engineer, or the director, to "duck" the sound of that car engine, so we can hear the dialog...
Or, as in some modern movies, to choose realism over intelligibility, and deliberately allow the dialog to get drowned out from time to time...
And to make that grenade explosion loud enough to be jarring but not too loud...
(But, if they didn't do a great job, or we disagree with their priorities there, there's not much a few more speakers are going to do to improve the situation...)
There's also the little detail that, whether it's because of budget constraints, or the size of the holes you're willing to put in the ceiling, there is USUALLY a trade-off between quantity and quality...
In short, you're almost always going to get better sound quality with fewer speakers of higher quality, rather than with many low quality speakers.
The main reason for using more speakers is to increase the number of seats having a great ATMOS experience. Consider having a row 5 seats across where the right and left seats are only 3’ from the side surrounds. With a 7.1 system a car racing passed you on the right going front to back may sound exactly as intended in the center seat. But sitting in the far right seat the car starts off coming toward you, hangs at the side surround getting louder then softer, then heads to the rear. Depending it might sound more like a jump (front->side->rear) then a transition. By adding more speakers the movement of the car can be smoothed out even for those extreme seats.
My suggestion is to put in the minimum number of speakers you think you need and have a plan for how to add more if you need to.
