Let's be generous and say the average Netflix (for example) viewer watches 1 hour per day.
At £6 per month, that's 0.20p per day, or 0.20p per hour.
So if all content providers were to,charge, say 0.20p per hour for their mainstream catalogue, or say, 0.40p per hour for blockbusters or what they class as premium content (the BBC colour TV license is almost exactly 0.40p per day), then it wouldn't matter if we needed multiple subscriptions to multiple providers.
If however, they all charge £6 per month, someone's going to lose out somewhere.
The consumer will lose out through being unable or unwilling to pay for access to all they content they want to watch. Some content providers will lose out to others because they're not in the viewers discretionary budget.
If providers harmonise the price per minute watched, they could also sell that to other service providers in bulk, similar to existing agreements such as MVNO etc.
Fragmenting is a bad move and will ultimately lead to a loss in revenue unless the price is harmonised at an affordable rate.