Havo, I feel like a lot of your points are built on the idea that borders in EVE are porous and that allowing massive naval battlegroups in and out is an easy, everyday occurrence... even though they have to come through specific, easily-monitorable stargates, and that the operators will be to stupid to recognize easily noticeable trends
We live in a world, right now, you and me, here on Earth, where exactly what you just described is a regular occurrence. I mean, you can't prove a negative, so without entering into the realm of logical fallacies let me ask you: do you believe for one moment that the only US operators in the Ukraine are the ones openly publicized on the news, or that Russia doesn't know about the US operators that are there?
"Operators" and "a huge naval battlegroup" are two quite different things. We aren't talking about a few stealth bombers and covert recon ships penetrating borders, which is something I am absolutely certain happens all the time, but significantly-sized military forces that couldn't be missed entering. Keep in mind, the Gallente Tripwire system was designed specifically to detect and handle intrusions.
The Iyen-Oursta loophole described in the PF Morwen quoted provides the explanation for how/why [Faction] ships come to be inside enemy territory. Quafe hired Fed Navy to escort the supply convoy to that Quafe outpost in Lonetrek. Great! Now that they're inside State borders, they set up whatever they set up, or they start undermining whatever they start undermining. Or whatever they decide to do. Are they tightly monitored? Of course they are - how else could Agent X at Lonetrek L4 Mission Hub Y send Capsuleer Z to go fuck them up?
It brings a perfectly good example of what it could have happened
once, but still puts the response and the fact that it is allowed to repeat firmly in the realm of lore-gameplay segregation.
Why do they continue to allow Fed Navy ships into their space under the Iyen-Oursta loopholes? I can think of a variety of reasons:
1. It's more trouble than it's worth to violate the treaty by refusing to let them cross the border. This would require either pulling the leaders of the 4 Empire Powers to the table to renegotiate, crippling economic sanctions or outright war for breaking the treaty.
So, uh, it's less crippling to have multiple hostile battlegroups repeatedly go rogue within your territory? Not to mention that even a few ships intruding across borders have been treated as a major violation of various treaties; why would even larger forces not be treated as a violation of other treaties?
2. It's much easier to just send one of the thousands of capsuleers available to go fuck them up.
Another instance of lore-gamplay segregation: Capsuleers are not, by lore, all-ending gods who can singlehandedly wipe out naval flotillas. That is a product of the player ship power-creep over the years. Moreover, by lore, the navies have their own capsuleers in even greater numbers: Why not just send a couple of navy capsuleers to handle it if we are so good at it?
3. Not only is it easier to send a capsuleer to fuck them up, it's also cheaper than sending their own Navy taskforce to fight the "rogue" elements of the enemy Navy and cheaper than renegotiating, suffering economic sanctions or outright war - which, by the way, would likely be sparked by sending their own Navy to eliminate the hostile force to begin with. Sending a capsuleer costs them a couple million ISK and a few loyalty points. Sending a Navy taskforce and replacing the losses incurred thereby would cost hundreds of millions, possibly billions if it goes poorly.
See above about navy capsuleers, but I also have to question the idea of not responding to cross-border incursions because they might be bad PR: Not wanting to immediately jump to open warfare I can understand, but not mentioning it whatsoever? That doesn't seem very logical, and stands as another point of lore-gameplay segregation.
4. What's not to love about watching a capsuleer fuck up an entire enemy Navy taskforce? Especially when you know that:
See above about navy capsuleers again.
5. The enemy Navy would absolutely not dare doing anything that would break the CONCORD treaty itself and escalate to full-scale war.
Like, uh, engaging in hostile cross-border violations with significant fleet assets in a direct violation of the treaties? Remember, two battleships crossing the Caldari-Gallente border was a huge deal - and they didn't even shoot anyone. If two battleships is an international incident that was widely recognized and treated with appropriate weight, why not these other incidents?