If you are BJP supporter , i will try to give some reasons :
1 : BJP got massive majority . They need someone who can control 300+ MLAs and who is acceptable to all caste and communities who voted for BJP . Eg Rajnath Singh was a good choice but everybody in UP will see him as Thankur CM . Yogi has advantage that he will be seen as Hindu CM only . So both upper castes and lower castes will be happy .
2: By making K P Maurya deputy CM BJP is making OBCs happy . Other deputy CM will keep upper caste happy too .
3: Number one issue in UP is law and order . Yogi can run tight administration similar to Maya .
4 : Any outrage by media ,"secular" and "intellectuals" on Yogi and his statements on Ram Temple etc will help BJP . Most UP BJP supporters support BJP on these issue.