Why are they attacking Obasanjo for endorsing Obi?

It is no more news that Obasanjo has picked his tent with Peter Obi as his preferred candidate for 2023 presidential election, bt i really do not understand why other politicians has been attacking the old man left and right because of Obi's endorsement. Not too long ago, the other 2 major aspirants paid homage to Obasanjo's house and it appeared they were all in good terms with him but immediately the man picked his candidate, he became their enemy and they started attacking him. I dont understand why because he cannot support the 3 of them at the same time and he has made his choice even with enough reasons. Why do you think the man is being attacked and assaulted, your opinion please?