And yet he didn't start trying to destroy Lyoko until the season started? Lazy.

hmmmmm. I agree. Maybe, but they'll never like do anything to like get them out of the thing... Wait...is Jeremie in the bubble? I never really paid too much attention to the episode

He is. He went to Lyoko to find the others in the episode.

Perhaps in the end, Aelita didn't destroy the bubble, and XANA faked its destruction on the inside, but in reality, they're still in the bubble.

Perhaps the constant use of reused scenes are actually more than just lazy animation. Perhaps the simulation bubble just resimulates familiar settings and actions over and over again.

Further more, several of the Lyoko battles look like repeated battles except in a different sector with the background changed. Just look how many time Odd flies around a tower on the overboard in season 2 for example. 

I wonder if this ever occured to the characters?

Probably not. After they got used to fighting and started getting cocky, XAXA stopped toying with them and faked his defeat. Gave them a false sense of security, and when he got bored, he launched another "attack". On the outside, the world is in shambles because of XANA, but they're just relaxin in the bubble.

That would change...... EVERYTHING!

Interesting theory. I can't find any way to disprove it.

I do not like playing the devils advocate all the time, but disproving the theory is not that difficult, interesting though it is.

First off, XANA does not seem to be subtle enough to run a double layered “matrix” scam like that, especially in the first season.  If you look at the story arc you can see a clever metaplot development as the machine learns more over time with experience and XANA was not that clever in the first season.

At first it made attacks very directly, in a kind of traditional “killer computer” style but that did not work against the Warriors like it presumably did against the Project personnel and it paused for a week or so and started what appears to be going down a list of standard movie classics launching them randomly as it figured out how to accomplish the mechanics of them (which was probably the writers doing a nod to each in turn).

After months of that resulted in failure it stepped back and analyzed what happened and developed a new angle of attack for the second season, showing a little more flexibility in its actions mixing more complex plans with periods of frequent simple attacks to try to get the team off balance and adding the meta goal of stealing Aelita’s memory “keys”.  X.A.N.A probably did not even think of leaving the supercomputer in season one, it could have accomplished its goal without doing that if it was not blocked time and again by the Lyoko Warriors and  started looking for a way around their interference.

Again after months of that it sat back and looked over what had transpired, this time for a longer time and again changed tack for the third season,  and again for the fourth, each time getting more clever and focused but still not quite up to human levels of creativity.  Its pinnacle in the fourth season probably had a lot to do with it having William as a (partial) resource and even then it still had a machinelike OCD constraint to its plans and strategies.

The Ninja arc brings out this difference between human and machine directly.  The Warriors always lost to the Ninjas before Ulrich realized they were not AIs but rather avatars with human minds like themselves.  Since then fights between them have been more even.   The point this brings out is that XANA is a machine and thinks like one, and it cannot truly replicate the subtleties of humans.

The single level of craftiness shown in “Ghost Channel” fits the first season XANA style very well and the glitches seem to be about right for XANA at that time while a double level one would be well beyond its abilities to sustain for long even if it was able to conceive of it in the first place.

Sissys hair is a non-issue; she could have simply joined the ranks of the bottle blonde.

My theory on why X.A.N.A. never once attempted to steal Aelita's keys in season 1 is because he did not know they existed in her. If you think about it, when X.A.N.A. attacked the tower during her first virtualization, he didn't just take something from her, he found something useful in her. He realized that if she had the keys out of his little prison, all he had to do to win was get rid of her.