No, the big festivals and events causing the signal to collapse. You have tens of thousands of people with phones, which whether you are receiving a call or not are still sending and attempting to receive signals. The network can't handle the data and just locks up.
The 02 arena is fine because it is a) sponsored by a phone company and in a location that often requires many thousands of people to be able to use their phones. For festivals, you are in a field which normally doesn't have tens of thousands of people in it, and so the phone networks don't supply the equipment for that many people to connect to their service.
Until the technology exists to highly concentrate the area being blocked, it will always be illegal.
Having worked 8 show weeks (and more, most I've done is 5 performances of a musical in 48 hours), it didn't really phase me much. You accept you leave a normal life at the door when you start working in theatre. The big sings use alternates, and understudies allow holidays. I never heard any company member asking for less shows. More shows = more money. And in theatre, your job is sadly almost never permanent.
FOH jobs aren't too hard to get, well... it's luck and charisma and putting yourself forward and being able to shine in a group interview and more. But If you are interested in theatre and can prove you have people skills then you are in with a good shot, but the smaller the theatre the higher the chance of a job. FOH also means you will meet a variety of people doing jobs you didn't even know existed and find out if any of them particularly interest you,
But if you are interested in the management side of theatre, I'd start writing off to production companies and theatres about internships. It'll soon tell you if you want to work in theatre management.