This is technically a Discovery question, but as it’s a tech-specific one I figured it belongs here instead: Per a reference this week to interference the EDF encountered at Mars, apparently during the period of its succession from the Federation, Earth forces were still able to reach as far as Mars — but not as far as Titan, otherwise the species-identity of the raiders from Titan wouldn’t have come as such a surprise to them. Obviously this is down to inconsistent writing. Take that as accepted, there’s no need to repeat it. But in-universe, what would lead to such a weird, seemingly arbitrary limitation on what Earth forces could and couldn’t scan within the Solar System?
They should be able to easily scan everything in their own Star System. The only reason they couldn't is if somebody put up sensor jamming tech. But if the folks on Titan who were masquerading as Aliens did such a thing, I wouldn't be surprised if they caused that kind of interference since they were attacked by humans and for whatever reason, decided to portray themselves as "The Bad Guys" and wear those "Alien Masks".
So say, Earth raided Titan for resources (or otherwise took them) way back after the Burn, so Titan responded by faking a takeover by “deadly alien raiders” to discourage further raiding, set up permanent jamming, then started hitting stuff in Earth orbit themselves? That could work, assuming their own ships were also scan-jammed (which I guess they must have been) and they instituted a strict “self destruct before capture” policy for the sake of Titan’s security.
Earth is HUGE, they also have a planetary shield & it's own personal defense fleet. There was no real reason to raid, they were reacting in fear by attacking first, asking questions later thanks to "The Burn". Literally the reason they started the entire stupid fight, because they lashed out in fear and didn't think to communicate & ID first. Ergo the years of unnecessary blood shed of human on human violence.