Why has the BBC given away 75% of a Multiplex to the commercial sector?

One effect of the Freeview retune was the BBC just giving away bits

^{Brian Butterworth published on UK Free TV 3rd October 2009 at 16:47}

Just looking at who has gained and lost in the Freeview retune.

• ITV. One slot lost on PSB2, a quarter of 40%, ie 10%. Gained 25% of Mux PSB3. NET GAIN 15% of a Mux.
• C4. No losses. Gain 25% of Mux PSB3. NET GAIN 25% of a Mux.
• FIVE. Loss of 10% of COM4, Gain 10% of PSB2 and 25% of PSB3. Net gain, 25% of a Mux.
• BBC. Loss of 75% of PSB3. Gain Nil. NET LOSS 75% of a Mux.

Just wondering why is it OK for the BBC to just give away valuable Freeview bandwidth.