The headline on John Harris' article on the prospects of moving parliament "Parliament is falling down. Let's move it to Birmingham" (9 September, https://www.theguardian.com/commentisfree/2016/sep/08/parliament-falling-down-move-it-to-birmingham) is misleading, as Harris is arguing to move the House of Lords out of London, not the entire parliament.
The difference is important.
As most ministers are also MPs, they need to have the legislative house close to their departmental offices, as they both regularly work part of the day in their ministerial office, ands part of the time have formal and informal duties in Parliament, including answering routine oral and emergency questions ( of which they are given short notice of a few hours) to MPs; appearing before select committees, meeting lobbies and attending events organized in Parliament.
Peers who are ministers also do these things, but are usually not the lead departmental minister, so could always belatedly inform the low upper house of peers.
The magnificent library would have to be split up.
With Parliament in the UK's capital city, many organizations which regularly interact with parliament have similarly located there Thus most non governmental organizations/pressure groups, trades and professional associations and institutions, trades unions and many think tanks are based in London.
Harris clearly spends a lot of his time reporting politics from outside London, so may not appreciate how important it is to co-locate parliament and its collective - and very important for democracy - lobby.
That's why not.