I have noticed a change in the hay quality this year for sure.
I buy my hay from timothyhay.co.uk, and usually get the 'Soft timothy hay' which is currently from the 2018 batch. I went for a 2020 timothy batch and my two wouldn't eat it! So I ordered the 2018 again and they wolfed it down. The weather this year in the UK was awful for hay production; periods of being very wet and then very hot and dry.
Hay definitely varies with weather! And if farmers have poor weather for hay and produce less, the price will go up. Supply and demand etc.