So why do we need to practice gratitude? Why isn't it innate?

It’s a part of our evolution. We generally tend to return to a certain baseline level of happiness despite major positive or negative events in life. We adapt to them. This concept is called “hedonic adaptation”, and it is essential for our survival.

The downside of hedonic adaptation is that we also adapt to even the most wonderful things we have over time. Their subjective impact decreases over time, and we lose interest. There are many things in life that make our lives much better but eventually we don't even acknowledge their existence because we get used to them