I can't say i have seen that many traps, they have some traps troughout theyr various ruins, but its by no means a minefield, and considering the dwemer seemed way ahead of theyr time, i am sure they had a mechanism that allowed them to keep this traps offline while they were present.
And I don't know why people keep saying they went extinct.
I for one felt that the mainstory kind of gave you a small insight into how they disapered.
Spoiler The Elderscroll that is later used view the past, and was most likely the scroll that sent alduin into the future is located in a dwemer ruin, inside a dwemer device. The dwemer disapered without a trace, much like alduin did when the elderscroll was used against him. Personally I feel its rather obvious that the elderscroll had a direct connection to the dwemer disaperance. I would not be suprised if the dwemer appeared in a Expansion or in the next TES, judging by the fact that the elderscroll was located in a skyrim dwemer ruin, I feel/hope it would be logic to assume that is where they will re-appear in a expansion rather then a future game
So if I am correct, it would also be logical to assume that the dwemer had plenty of time to reactivate theyr traps.
Also since the dwemer were in a ongoing war the falmer when they disapered it makes perfect sense that they would make these traps.
Edit 2: Dwemer ruins not making sense for living quarters? chances are most of what we have explored are service tunnels, and other various stuff.. Markath is a pretty good example of how a dwarwen city might look, and that is plenty functional.
Edit: And yeah i agree the dwemer ruins can be a pain to explore, but not because of theyr size, for me the problem with them is that theyr mostly just inhabbited by boring machines that dont bleed when i kill them

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Once you get to blackreach how ever you will most likely be awe-strucken. not to mention its much more intresting since the falmer do indeed bleed *grin*