Why do disillusioned MP's not just defect to another party?

The coup organisers should move to another party.

The Parliamentary Labour Party have chosen now, of all times, to declare war on the party membership to gain control of the party.
At a time when the Conservative government is fragmenting, but is still able to inflict hardship and division on the people of this country. At a time when the conservative party itself is in the turmoil of a leadership election, the self serving opportunistic PLP seek to overthrow Jeremy Corbyn and force his resignation rather than challenge his position by adhering to the democratic party rules to bring about a leadership election. They would rather fight their own party members than unite and face the real enemy opposite them in the House of Commons.
Many people cannot understand why, if these MP's are so disillusioned with the structure and course of today's Labour party, that they feel so frustrated at the party's emphasis on policies rather than personalities that they do not just leave the present party and join another more in line with their own personal beliefs. The reason that many in the PLP remain, is that they enjoy the benefits of our party organisation, enthusiastic members to canvas and organise elections, financial support from unions and affiliates and everything else that the "Labour party Candidate" description brings with it. They could not afford to run their own party and would be unable to accept the fall in their personal stature and position if they joined another and so remain in ours to conspire with each other and plot the removal of anyone they don't like. Why should we hand them our party on a plate by resigning? Let them join another or create their own. It has been the same with some elements of the PLP for many years. Patronising and arrogant, they seek to preach that they alone know what is best for party and country, that they alone have all the answers, only they are capable of controlling the party and that all party members must accept their instructions without question or resistance. In all my years in the Labour party, this is the only time that I can recall, where the rank and file membership have actually taken a stand against the self serving elitists who have dominated and controlled the PLP for far too long. 
I, and I am sure thousands of others, will continue to support Jeremy Corbyn in this struggle for the very heart of our party.