This isn't really true; scientists also praised Einstein for his deep mathematical intuition. His work on Brownian motion and general relativity was new and difficult mathematics (GR still is). GR is also startling for the mind-bending fundamental intuitions behind it. He asked mathematicians for help hammering out details, but 1) everyone does this and 2) mathematical rigor and abstraction wasn't nearly as well-established back then as it is now, and was difficult to grasp for many physicists and even mathematicians. For example it was several years before Minkowski established the connection between special relativity and the "shape" of spacetime, giving rigor to Einstein's intuition--but doing so is nowdays an easy exercise in undergraduate mathematics.