I think it's just a case of that custard being tight. 
I bet if you'd put the price rise in place every year for say 30p increase a time, they would have said......"what? Again? You just put the price up last year"....
With some You just can't win. 
I can't find it now, but there was a study to show that generally customers prefer bigger rises in price less often, rather than regular small increases. 
Some pschycology in it I guess. 
I'm at the stage now where I really need to put in some price rises. Some places haven't been increased in 5 years. 
 
 But then again I'm also quite happy to lose some and replace with better paid work. I'm pretty much flat out with work now, so need to
Do something.