Learning is a process of identifying similarities between something we know and something don’t (the thing we are learning). Learning brand new things is usually hard, not because it is more difficult, but because we don’t have similar things to compare it to.
When you first learn how to program it’s really hard. The similarities with things we know are very limited and not similar. Once you learn how to program, it’s much easier to learn a different language. Some languages have more differences than similarities (e.g. functional programming) but there are still enough similarities for us to know where to start.
The more variety of experiences you have the easier it is to have similarities to learn new things. Having a deep knowledge in one area is good for some people, but having a broader variety of knowledge will help you innovate more than people with narrow expertise.