I've been a freelancer for a long time. There is always that tug of war between writers and editors. If I had pitched something and it was accepted, I would not withdraw it. But it is a risk worth taking at times.

It is a good point to not burn bridges. Its a tricky balance at times. I do simultaneous submissions at times, but if one shows interest i try to back off the others.

I get that its frustrating for editors, but having to wait a long time is frustrating for writers too. Its a tension we will have to live with. :)