I don't think Bright offers options, but if he wanted to chime in here that would be welcomed.
Mostly, I would guess its probably because most of the firms generate a portion of their fees from transactions and there are times where several days go buy and I'm not making any of the necessary adjustments, (raw delta hedge, adjusting wing risk, changing forward vol perspective...ect..) so while these are generally very profitable days, they are also without fee income for my broker.
Secondarily, even listed options are considered complex instruments, and if a trader starts using a complex multi-expiration multi-insturment hedged book, it is probably a bit beyond what most of their risk managers have experience working with and so because of the non-linear aspect of options, it would be more difficult for these small shops to understand their net risk. Not impossible, just more difficult.
I really wish there were more firms out there which backed experienced options traders. It could simply be that experienced option traders are in short supply.