Why appoint another peer?

Minor reshuffles have gone almost unnoticed amongst the fuss as to who is 'running the country' during August (we never used to have this nonsense. Why do we have it now? Does the country genuinely need 'running' like this? Is it, perhaps, illustrative of the undermining of Cabinet government if we have to have a primus inter pares at all times?).

One of these minor appointments has been that of Lord Brett (who's last post before becoming a life peer in 1999 was being the general secretary of a trades union I'd never heard of but has now, after merger, become Prospect) as a Home Office Parliamentary Secretary in place of Meg Hiller, whilst she's on maternity leave.

Lord Brett may have merits but he's hardly shown the form to be a weather changing appointment a la Mandelson. So why, does a Prime Minister desperately in need of approval and endorsements from anongst his own Parliamentary (for which read, House of Commons) Party, pass up the opportunity to give a bauble to an MP, and instead give it to a journey-man peer? Brett doesn't have the sort of specialist skill or reputation that doesn't exist in the Commons, he's not an independent GOAT who can demonstrate what a consensual sort of chap the PM is. A golden opportunity to, at the least, get another MP on the payroll vote, grateful for the opportunity and experience passed up for, apparently, nothing.

Why?