Avoiding them is one (usually not too hard) thing. But it comes at the cost of precious time, time in which those turrets can pick of the turret and AI fighters and end the attack phase before you can really do much. And all just because of lazy / not well thought out game design. Even worse if those turtles have a brain as @Petersaber mentioned. Just because you're lucky enough to not be plagues with such behaviour doesn't mean it's an issue.
So I think the OP was talking about all forms of sitting still and shooting, not just specifically camping behind shields.
I really think that people do this because it's easier to control, not because it's actually giving you an advantage. And the thing is, it does give you a disadvantage because you turn rate goes down, so you can't aim as well against fast targets, and you are very vulnerable because you're sitting perfectly still. Against decent players it just doesn't work. It counters players that fly in straight lines directly at their target, because they are now easy targets themselves.
And on the topic of it taking more time to evade or go around them... well isn't that true for someone actively defending by flying around and trying to cut you off or get behind you?
If the issue is that it actually takes too much investment to kill people camping behind the cap ship shield, then the shield itself or the timing window of the attack phase needs to be adjusted... because you can just as well utilize the shields on defense while also flying at full speed. So either make it so shields block shots both ways, weaken the shield strength, have the shield only protect the capital ship, or increase the time that the attack window is open, because it does feel short regardless.
So basically I just see this as a non-issue. It's like complaining about people that camp with an AWP, where the solutions are very similar: use movement, and use your utility.
