Why did India play Sri Lanka so many times from 2007/08 to 2010??

Aren't sides supposed to tour each other at an interval of 4 years. That clearly was not in the case of India and Sri Lanka.

I'm not sure how many of you (followers of India-Sri Lanka) have noticed this, but the amount of time we played Sri Lanka (Red mark) during that phase was quite overwhelming. For someone who started watching cricket during that phase, I always wondered why we play so much against Sri Lanka. After a while those matches became so boring and lost all the hype. In the 2011 WC final I wanted NZ against India because I got fed-up of India-Sri Lanka finals🥱

So, was there a reason for that? Does anybody have any idea?