Seriously, WHY??

Do note, I'm talking specifically about lore here. From a gameplay perspective, I get why Bethesda chose to keep dragons after the main quest; for players to continue collecting dragon souls needed.

But lore-wise, is there any sense to this? Alduin resurrected the dragons in the beginning and I know, there's probably still some dragons remaining alive. But why do these remaining dragons still attack towns and cities?

If you do the main quest and Paarthumax is kept alive, he'll tell you he's taken the place of Alduin and now controls the dragons, so shouldn't that mean the dragons will be peaceful? Unless Paarthumax turns villain, which makes no sense either because then the Dragonborn will be tasked with stopping him.

Can anyone give a logicial explanation on this matter, or is the ever on-going dragon attacks really just for gameplay sake here? Personally I gotta say, it kinda breaks the immersion on my playthrough, where the main quest has long been completed...

Since it's a Lore question, I'll move to the Lore forum.

Because the gameplay reason is obvious (you need more souls to unlock shouts,) and won't answer your question.

Because while you were studying alchemy, Alduin was reviving
While you were enchanting, Alduin was reviving
while you were making jewelry and weapons, Alduin was reviving.

From the UESP " If you did not already kill http://www.uesp.net/wiki/Skyrim:Paarthurnax_(dragon), he will have a final conversation with you, and expresses hope to convince other dragons to join theWay of the Voice. Afterwards, if you are still on the mountaintop, http://www.uesp.net/wiki/Skyrim:Odahviing will come to admit his allegiance to you so that you may freely use his Thu'um to call him, though he warns that not all dragons are willing to follow Paarthurnax's example."

So, Paarthurnax does not have (nor claim to have) control of the other dragons, he just hopes that at least some of them will come and be chill dudes with him. Odahviing specifically says "mate, Paarthurnax is maybe a bit optimistic, yeah?" And, well, dragons tend to be arseholes bent on destruction of humans, innit?