All languages change over time. But the rate of change is dependent on a lot of factors. Purely spoken languages change the most over time. Languages that have a long written tradition and most children are in school (as opposed to working on a farm or in the family business) tend to change slower as people are more connected to older forms of the language.
Purely spoken languages change much more quickly because the normal forces that make language change are not being held back by widespread education and literature. Languages change because people start speaking differently because a role model starts speaking differently for fun, and their change catches on, or because an academic proposes a change, in any case, there are many reasons why people would start pronouncing things differently.
Once people start speaking differently, they will be others who remark upon this and say things like, “The language is going to the dogs” or such things. This has never been true. Languages change all the time. It doesn’t mean the language is degrading. Once the changes in the language have become more widespread, it will start being picked up by younger people. Since they grow up with the change, it will become normal to them. And then they in turn will make new changes, and so the cycle of language change continues.