Different networks structure things differently, O2 (and most of their and other MVNOs) seem heavily focused on acquisition and use roaming and low cost SIM offers as the cornerstone of their pitch to try and improve their market share and retain what they can.
There is less of a focus on the quality of their network and, even if they had speed caps, they have such congestion and poor infrastructure (at least in my experience when I was with them and through family more recently) that you would struggle to reach those speed caps apart from in select urban areas.
Yeah the plan you are on is 100% not a tariff that EE are actively marketing to consumers, just a backbook retentions one they can use to discount to an appropriate level. Doesn't matter how they get down there if they can get there.
In fairness the full prices of the Multi Product Plans are notional too, as EE don't sell 30 day Unlimited tariffs for those £30, £33, £36, £42 and £48 price points to someone without EE Broadband and then they're discounted £20.
