Why are companies so prejudice about hiring a female Crane Operator?

I have companies that will call around begging for a crane operator to my male buddies. When they suggest me, they tell them oh, okay. This company I work for alot said they got alot of calls everytime they sent me to a plant. They were saying, ';What's up you sent me a woman?'; But this company always told them ';Give her a chance, she's an excellent operator';. And they told me they always go excellent reviews back on me. But must about 85% of the companies will not hire a woman crane operator. I have had companies go from leary about putting me on a job, to requesting me. But because I am a woman alot of jobs won't send me out or hire me.To be honest alot of men tell me I am the only woman crane operator they have ever seen. . Why do they still do this in this day and age.? It is so unfair and hurtful.