Sometimes two consecutive contests have a gap of around a week between them (maybe more)... And sometimes consecutive contests have no gap and are held in consecutive days.. Please check recent contests history..
Why not to schedule them having around a day or two between them?
Because that's CF style and doing it otherwise would be contradictory xD
I think most of the time when two contests are held with 1-2 days, some of them are mostly based on special events like a high school programming contest or VK Cup where you can't delay the contest to not have them leaked,etc.
I also think it's sometimes fun in general to do a lot of them in special parts of the year ( like the end of it).