One of the big contributing factors to poor singing has to be the use of directional microphones. The practice of singing so close to these results in the complete loss of plosives, fricatives and hard consonants with the result that the lyrics seem to be totally composed from vowels.

Another modern habit sems to be the stuffing of so many grace notes and vocal pyrotechnics into the song that again the words completely disappear.

Accent and phrasing can't be blamed for poor speaking and singing habits