Then why doesn't steam on PC charge a monthly fee to use it's many extensive services? Just because they've given a reason for charging for something, doesn't mean we need to accept it blindly.
Because Steam wants your business. They offer their services in exchange for you buying more games on their platform. Initially they made these services for their own in-house developed games on the platform.
The consoles that had online functionality before the Xbox didn't charge for it, with the exception of SEGA Genesis' system that worked through your cable TV provider back in the 90's (and was so niche, not many people outside Japan had it). The Dreamcast and PS2 both managed to have online services similar to what Xbox provided, and they were completely free of charge.
I don't think they were similar at all. I loved the Dreamcast, but being able to play laggy games of Chu Chu Rocket on dial-up is not really a comparison to the dedicated servers, closed moderated ecosystem with chat/friends etc. that MS created. And that's just comparing to the early iterations of Xbox Live.