the common thread I see with this year's fatalities and earlier ones too is: These are people from out-of-state, not familiar with Mt Whitney, not familiar with the Sierra, little or no experience on other Sierra trails. Maybe these things add up to a higher possibility of making big enough mistakes to lead to disaster.
The only common thread this year is they were hiking alone. Mr. Likely had experience on Mt. Whitney. I do not know enough to say anything about Mr. Johnson's experience in the Sierra or experience in general.
A SAR friend of mine has switched away from solo hiking is ok after rescuing too many solos.