Strobe lighting, even the most powerful, can easily be rendered ineffective during daylight especially in low-lying sun and conditions of glare. Daytime fog can also EASILY conceal hazard lights. Strobes in fog refract among the moisture-laden fog particles creating a weak short range luminescence which is normally only visible from any distance at night.
As Crab has said, obstruction lights tend to be at the summit of an obstacle although for buildings and obstacles above a certain height additional lights are required at intervals along the length of the obstruction.
Either way the spacing would not have been sufficient to warn the pilot of the crane jib where he hit it and the field of luminescence from a strobe surrounded by fog would only have been visible a few feet away from the obstruction during daylight hours.
To support Crab and others who have said the same, this is NOT an issue about lighting especially given that it was a daytime accident.