I've always wondered this. I think the topic came up in the Skyrim forum a few months back, and (disappointingly enough) the 'conclusion' was that they simply wore away.

Yes. In just 200 years.

Of course, this wouldn't be the case, as, well, these processes take a LONG LONG time, at least thousands of years.

So, did the Nords dismantle the gates? Did wizards of others of the like take them apart and use the (possible) residual Daedric magic in them for research? Did they just svck themselves back into the ground where they spawned in the first place?

The lack of Oblivion gates in Skyrim can only be attributed to the same cause as the lack of Falmeri ruins in vanilla Skyrim: 11/11/11.

I'm sure there is an explanation... they destroyed them or got rid of them somehow.

"Wizard did it" - Bethesda.

I really hate this excuse, but I'm pretty sure it's accurate in this scenario... 11/11/11.

They were all knocked down, of course. Nobody wants them lying around as a reminder.

Oblivion gates, like everything in a realm of Oblivion, are made from excess creatia. However, due to the pact with Akatosh, material from Oblivion is inherently unstable in the Mundus. When the Pact was broken and Dagon invaded, the gates were able to become stable.

When Martin/Akatosh banished Dagon and resealed the pact, material from Oblivion once again began to be rejected by the Mundus.

Thus all gates decayed quickly after the end of the crisis.

What is this based on?

I imagine after hundreds of thousands of people were killed as a result of the beings which poured forth from the gates, the locals would like to get rid of any reminder of such a terrible event and the symbol attached to it.

There's certainly no shortage of bandits throughout Skyrim, hoping to make gold any way they can. Give 'em pickaxes, and I'd say those ruined gates would be chiseled down in no time. That otherworldy rock/glass has to be worth something.

Still, there are Daedra fanatics everywhere. I'd be surprised if there wasn't a shrine built around one. Seeing one make a cameo in a Daedric quest in Oblivion would have been awesome, but oh well...

I support this as Betheda's cop-out.

I highly doubt that this was caused by a lack of time on Bethesda's end. I mean, all it would take is a quick model and texture, and I can guarantee "Where are the Oblivion Gates?" was a question asked very, very early in development. They probably chose not to include them because they wouldn't serve any purpose aside from confusing or alienating players who didn't play Oblivion. Just standing there for no rhyme or reason save to satisfy the one or two players who would take a moment to question it. Simple marketing. Can't force anything on those who aren't yet interested in the lore.