Modern media is less about the information and more about the hype. The journalists could do that maths easily but would that raise hype and earn clicks? Of course no. Their bread and butter is mainly controversial news, even despite them being state-funded.
It will be, but that is not the original agreement. The original agreement was a number of shares that they could redeem within six years - not the plain £75m (used to be £100m) figure. There is no reason for BBC to shame the company for doing good business. Shareholders understand it and do not complain too much. But the general public will pay more attention to the final sum rather than maths and years of work behind it. Persimmon CEO’s actual salary rate is mere £675,270 with a slight bonus of £1.3m.
To look at it from another perspective, imagine your employer says that he will pay you a standard rate of £30,000 a year and a commission of 1% based on sales you make. You are great at selling and your sales amounted to £10,000,000, hence you expect £130,000 to be paid. But the employer says “sorry mate, I give you £80,000 and you should be happy, that is a lot anyway. Cheerio”. Oversimplified but similar gist. If something has been agreed, there is no reason why the agreement should change in case the results are too good.