Part of the issue is cost.
One or two per car?
Times 130 pieces of rolling stock (less locos)?
Cut a hole in the floor of your EXPENSIVE hand-built 1:20 wooden passenger coach?
Tank cars will be fun.
For me, not worth the effort.
I am guessing there is the same vocal minority that resulted in a certain Socket that have hollered for this.
To give you an idea, the outfit I work with has had remote control of turnouts available for, oh, 12-13 years or so.
Not a lot.
Folks in the field who do this don't care, don't want it, don't want the extra maintenance, are quite happy with manual throws or EZAir.
Same with couplers.
Maybe on the loco, but if you're dropping off car #3 in the string, then you have to have all of them so equipped.
Now, if this transmitter is addressable to any specific car, great.
But, if one transmitter triggers all of them, and you want to drop one car that is 3 back in the string, you back in, hold the button, pull away and leave the entire string.
Let's say it's addressable by car number.
The average age of Garden Railroaders?
You want to drop that third car.
You end up walking over to the train to read the car number anyway.
Going to disassemble all your rolling stock and replace all those 9V cells every operating session?
Duracell, with tax, about $2 each.
That would cost me $260 per session, on top of the cost of the uncouplers, installation, AND mounting Kadees on all my stock, just to be able to "do" it.