Dairy and gluten are not "bad," but a lot of people have issues digesting them and they can cause inflammation in the body for many people. The recipes on my blog are primarily dairy and gluten free though, but they can be adjusted to suit anyone.
I also write my meal plans this way because so many of my clients and customers come to me with inflamed systems, often caused by overeating processed foods. Many processed foods fall into the wheat and dairy category, and eliminating them, even temporarily can help reset the system.
I am not 100% dairy or gluten-free. I occasionally eat grass-fed, organic greek yogurt (plain and full-fat) because the fermentation process helps break down the hard-to-digest proteins in dairy. I also eat grass fed butter sometimes. I sometimes eat Ezekiel sprouted grain products, which are not gluten free. But, the sprouting process helps break down the gluten to help us digest, as well as breaks down the phytic acid in the grains (which hinders absorption of nutrients).
When it comes to gluten, dairy, or any other commonly irritating foods, it's always best to find what works for you - as well as looking for the highest quality sources to avoid unnecessary ingredients that can cause issues for your system.
There is no "perfect" diet - different things work for different people at different times so don't be afraid to experiment and see how you feel leaving these things out - you can always reintroduce them anytime.