This is deliberate
The classification scheme allows LLU operators to gain extra profits from mkt 1 exchanges and acts as an incentive for them to go into an exchange in the first place.
I'm not entirely sure this is correct, even if it sounds wonderful.
The Ofcom classification was done based on both the knowledge of where LLU unbundling had already happened, *and* based on where the LLU operators were planning to exand to - though based on plans at the time.
If the classification was done using future plans, then surely market 1 exchanges would have jumped to market 2 or 3 well before the operators actually went live, and preventing these "extra profits" - totally opposite to the effect you describe as "deliberate".
For example, the Ofcom report on WBA (2010) made the following definition: "Market 1: exchanges where only BT is present or forecast to be present (11.7 per cent of premises)" with a footnote of "In assessing forecasted plans we have only counted operators as present where they have firm plans to deploy in specific exchanges."