It’s because the mechanism for adjudicating the high crimes and misdemeanors resides in the legislative branch. They have to adopt articles of impeachment and then convict and remove the President.

If any state crime felonies could automatically disqualify a candidate it would create perverse incentives that should not reside within the power of one state, because of the abuse potential. For example, Texas could drag Biden into court on felony jaywalking charges.