-
It’s challenging to do both, you have to be much more familiar with both the melody and the lyrics to pull it off.
Many lead vocalists in rock bands actually have (or had) guitar skills but would rarely play while singing on stage: Sammy Hagar simply wouldn’t play guitar while lead singing and he explained: “if I try to do both, they suffer”. His predecessor, David Lee Roth, has in fact donned a guitar on occasion. Robert Plant could play but did not while Jimmy Page was on stage with him. I’ve seen video of Mick Jagger awkwardly playing guitar on stage, but immediately stop playing when he started singing.
More often than not lead guitarists don’t sing or sing primarily backup vocals. (Pete Townsend, Eddie Van Halen). A select few can seemed to do both with ease but I imagine it comes from doing it a lot from a young age (Eric Clapton, Jimi Hendrix, John Fogerty, Peter Frampton, Joe Walsh, S.R Vaughn, Mark Knopfler, Lindsey Buckingham)