[1] reality is also somewhat in question in the films universe
At least that's my recollection. I've watched the matrix a few times :)
It's worth remembering that the Matrix is an allegory for systems of labeling and control (notably, gender), which make life (and specifically life with others) easier, though not necessarily better. The Matrix sustains the large human and machine populations amidst Earth's ecological collapse; people who choose Zion choose a harder life where they are free to be themselves. However, when Zion grows large enough to threaten the system, the system comes after its residents and wipes them out.
One person's freedom is tolerable, even necessary for the system to continue; everyone's freedom leads to everyone's doom. The movies have some weird-but-rational implications.
...Sorry, I lost track of my point, which is that we're already in The Matrix. The Matrix is society.
One individual human (Cypher) did choose to be plugged back in, though it didn't work out for him.
simulation becomes real enough
Riding a real horse isn't just about the horse ride, right? It's about the trip to the horse farm. The small but real danger. If you're doing it on some sort of multi-day trip, it's about the memories you make with others, the romantic time spent with your partner at night, or if you're single maybe the hope of meeting a romantic partner. For some maybe it's even about doing things like cleaning the stables, which isn't intrinsically fun, but probably adds to the feeling of bonding with the horses.
(I've never ridden a horse. I'm surely wrong about some of those things)
There's also the "abundance issue" with simulations. Have you ever looked at your unplayed games on Steam, or a folder full of ROMs, and just had a hard time choosing or enjoying anything, because (a) there's so much there, nothing feels special and (b) even when you're enjoying one game, part of you is thinking that perhaps the next game is even better?
If things truly progress to Matrix-style simulation, I guess a lot of that is "solvable" by "just" manipulating/injecting memories. But I think that's how far a simulation would need to go in order to supplant real life experiences entirely.
Or, there's the even darker route, also explored by much scifi -- reality gets so shitty that nobody can really even aspire to an actual horse ride anyway, so simulations are all anybody has. A lot of people already live some kind of version of this anyway due to lack of funds.
Sorry for no coherent point. Just rambling!
Reality is very much blurry
Right now we're fully on track for one of several dystopias.