Not to be an ass here but how about you think about it for more then 0 seconds and then come back and answer your own question.
Why would you have 1 campaign, 1 landing page with 10K keywords, 35 adgroups and 35 ads?
then
Why would you want multiple campaigns, with multiple landing pages, with LESS keywords and more adgroups and ads.
Some domains can get a higher CTR.... think about it. It IS apart of the ad.ok more ad groups... i get that.... but why more domains and more campaigns
There are many reasons for this and it makes sense.
Also consider that you get more control on a campaign-level such as ad-scheduling, geo-targeting, site-exclusion (for content), daily budget, etc. These are things you couldn't control on an adgroup level.