The £100 cut-off earnings limit is out-dated & has NEVER risen in line with the minimum wage, other state benefits or inflation.
Carers provide an invaluable service & save the government £119 billion p/a
carersUK
To qualify for Carers allowance you need to be caring for a minimum of 35 hours p/w - that leaves a lot of time for working age people to be able to seek some fulfilment outside of their caring duties, however with the minimum wage on £6.19 that restricts any jobs to 16hours p/w.
I find it a little out-dated 
but then this is a benefit that was only made available to married women in 1986

So am I being unreasonable to expect the earnings limit to raise with the cost of living?