I would if I could, I have hitch hiked one.
My 748 broke down on the motorway, a fellow biker on a HUGE touring bike asked if everything was ok. I told him I ran out of petrol (the light never worked and it was the first proper full ride I did). He asked if I was able to buy a can of petrol. Yes I was, jumped on the back of his bike. He rode me 3 miles to petrol station, I bought the can, rode me back. Bike was still there thank god. Filled the bike up and tried to offer him payment. Wouldn't accept a single thing, no petrol, no money. Nothing.
Legend of a guy, waiting until my bike started up, and off he went wishing me luck! Legend, absolute legend lol. Saved me a fair chunk of money in breakdown recovery!
Anyway, I did however stop coming off the M25 onto the M4 as a indian family's car had broken down causing a ton of traffic. Not a single person helped this poor woman with 4 kids to push her car. I stopped, climbed off the bike, in full leathers pushed her car to safety and called the services for her. She was in tears bless her. Traffic died down in the 10 mins I was with her helping to calm her kids down. Job done, on my way I went.
Oh! Also remember stopping by on a desolate road for a guy whose bike had broken down. Asked if everything was ok, he said the recovery was 2 hours late lol. I offered him a smoke, went to the garage, got him a drink and a sandwich, returned, we had a chat and a laugh for 30 mins until the recovery truck arrived. Off I went.
But yes, I would offer a hitchiker a lift. Why are people so scared? Surely you just stick to main roads/motorways?