Why would a boot maker move from town to town endlessly?

[Harry Randell]

Why would a family of boot makers move from town to town endlessly?
I'm tracking the Purnell family who are boot & shoe makers over several generations.  Joseph Frederick Purnell starts life in Cheltenham, and then has children in Bristol, Warwickshire, Glamorgan, West Bromwich, Staffordshire, Birmingham, Country Durham, Sunderland, Hartshill and back to Sunderland.  His brother Thomas follows the same pattern having children in Dudley, Tipton, Derby, St Helens, Gloucester, Newport, Cradley Heath, Birmingham and Ryhope near Sunderland.
When they appear in the census, the accommodation is always modest.
Having travelled endlessly for throughout the nineteen century they appear to settle in Sunderland.  Can anybody offer an explanation?  Is there a precedent for this as a boot and shoe maker who worked “own account”.

[Tricia_2]

There is a reference to a 'travelling cobbler', here. Maybe these men were the same.

http://en.wikipedia.org/wiki/Thomas_Sayers

[Harry Randell]

In the original question I forgot to mention they may have been making clogs, which I'm informed may be significant.

[RomanyRoser]

Hi- Robert DAWSON, lists the PURNELL family as travellers in his book  "A Romany  In The Family. Ïncluded here is the entry PURNELL 1826 (Somerset) (See Robert Dawson ARITF)- Roser

[Redskin blood]

Hello,

This probably needs more research, but sometimes cobblers or shoesmiths made boots for the
labourers and workers who were responsible for the excavations on the railways.
The railway workers were continuously moving around the Country as the railways were
being built and so the bootmakers job was to follow them around supplying footware.

[Harry Randell]

That does make sense. 
It crossed our minds that if you were making boot, shoe's or clogs you would need tools.  Hence how did they travel, coach, cart or walking and I noticed that on a couple of occasions their arrival coincided with the expansion of the railway. 
I thought they were using the railway to travel but it never crossed my mind that they were, as you might say, working in association with it.
Many thanks I will look into it further.
Harry