It so happened that after the Commonwealth Bank Series of 2008,then Indian captain M. S. Dhoni wanted a relatively younger team.
Seniors like Sachin Tendulkar,Rahul Dravid and Sourav Ganguly were present in that team.
While no one could ever question Tendulkar’s position in the team,as he was such a great batsman,and was definitely scoring at quite a fast strike-rate even at that age.
But Dravid and Ganguly,inspite of being in form,weren’t being able to keep pace with that time.
And young guns like Virat Kohli and Rohit Sharma were willing to prove themselves always,and rising very fast. Rohit had had a brilliant World T20 2007,and Kohli was always at his imperious best. So the selectors tried to invest in these youngsters.
Dhoni started rotating Gambhir and Sachin as openers,keeping Sehwag fixed in the opening position.
So the top 3 positions were filled up by Gauti,Viru and Tendulkar.
Dravid used to bat at no.4 in ODIs. And the form that Kohli started putting up at that position(yes,Kohli once used to bat at no.4) after 2009 simply closed the gates for Dravid’s comeback in the ODI side.
So both Dravid and Ganguly were dropped after this series,and soon fell out of favour in the limited overs team.
While Dravid continued to flourish in tests,Ganguly decided to take immediate retirement.
When Dravid did make a comeback in 2009 in ODIs,he managed a solitary half-century(76) in 5 innings,and thus did himself no favours to be selected again. And he played with a strike-rate of 69 that year,which was criticised immensely by several cricket pundits. And Kohli,who succeeded Dravid at no.4 position thereafter,was averaging some 55 odd that year.
After the 2011 CWC,when India flew to England to play the foreign series,Dravid earned a surprise call-up in both ODIs and T20Is.
He declared that it would be his last series.
That’s why he could play only one T20I,where he thrashed Samit Patel for three consecutive 6s.
So,it wasn’t a case of ignorance on Dhoni’s part. It was only that he wanted to make a young and strong team for the 2011 CWC.
Personal opinion- Dravid was striking at 83 in 2007. He could have done better if he had been given more chances. So dropping him in 2008 was a little harsh,as I would say. But he was already 35 by that time,and not getting any younger. Kohli,in his early 20s was full of energy,and that was the probable reason why they were preferred!