Why do plumbers avoid even refuse to work on mobile homes?

There is a good chance that they will not get paid.

I didn't know they did, but that's a bit stupid!

Because contractors refuse to work on mobiles homes. That will not get paid to them.

Most Probably they Dont Like Mobile Services,

Mobile home plumbing is notoriously difficult to work on because it is hard to get at, is sometimes substandard, and tricky to fix without special parts. 

Just the ones you have contacted.  Many don't do it as they specialize in houses so different plumbing size will be my guess.

They do? I've had no trouble getting a plumber to work on mine. Several times, in fact.

many mobile homes have poor quality clamped together water pies that don't meet codes cause trailer parks are not covered by local building codes. I stay away from trailer repairs. It can ruin my reputation when things go wrong in the future. 

Same reason I avoid working on oil furnaces in trailers.   Stuff is poorly designed an pain to work on .   

Probably dont want to risk having to crawl under it, when my family lived in a mobile home the kichen sink badly clogged up  my dad had to go under it and snake the pipe, he crawled out dirty with some spider webs on him.