Basically, the company which owns most of the last mile isn't actually an ISP itself - it simply owns the wires, and sells access to them to ISPs. They have to sell at the same cost to all ISPs. The telecoms regulator would block any plans for it to become an ISP itself. There's no weirdness about actually requiring that ISPs have an equal share of the retail market.

They do have a sibling company which is an ISP, but the telecoms regulator ensures that there's no preferential treatment going on.