What might compel someone to make their own language? Typically, it's because they've already used some languages, they have some criticisms of it, and they want to make something better. Now, for languages that are open source and accept community contributions, that is an option. However, keep in mind that each language already has its own core maintainer(s), with their own vision, as well as a whole host of other people who would have to be convinced that your idea (whatever improvements you want to make) are a good fit for that language. Some changes can be quite drastic — especially if you want to improve one language by bringing in insights you've gained from another. So sometimes (not often, but sometimes), people say "fuck it, I'm making my own language, with blackjack and hookers".

The thing about software is, it's really easy to play around with. You don't need a workshop or parts or anything — you just need your computer. As a result, you have lots of people tinkering with stuff like making their own programming language, whether just for fun or more tangible reasons.

And we've been in this cycle of innovation for decades, and it's how we've gone from punch cards to assembly to C, Python, and all the rest.

But surely we don't need any more innovation? Like, why can't we all just use one language for everything?

Well, it's true that nowadays we have a whole bunch of general-purpose, multi-paradigm languages. The analogy people like to make is "different tools in your toolbox". But, to clarify, it's not that some of them are hammers and others are screwdrivers; they're all the same kind of tool ("programming language"), so really it's more like different screwdrivers, of varying sizes, with differently shaped bits at the end.

With screwdrivers it's clear why you might need one with this shape or the other: Otherwise it won't match the screw. With languages it's a little more subtle. You see, when you design a language (or almost anything else, ever), you inevitably make a series of tradeoffs. Is the language compiled or interpreted? Does it have a garbage collector? Does it have a strict type system? How does it do async? Does it support higher-order functions? There's a million questions, and you're going to get a different combination of answers for each language you look at. And that's before you evaluate other (potentially very important) things, like "is this language fast enough for my use case?", or "I need a library for such-and-such, has someone made that in this language?", or "does the language have a solid enough community that I can reliably search the answers to my questions?".

Technically, any of the major languages — Java, Python, C, C++, C#, Javascript, Go, Rust, etc etc — can be used as a one-size-fits-all, universal programming language. There's actually a joke "law" that goes "anything that can be written in Javascript, will eventually be written in Javascript". But they each have their own unique combination of design decisions, so in practice different ones will be easier to use for this kind of project or that (one major factor is third-party libraries, like python's numpy or pandas, that may not have equivalents in other languages). There are also situations where, for a given platform, you have to use that language. For example, for Microsoft's .NET stuff, I don't think you can substitute C# for something like C++ (someone correct me if I'm wrong please). Or, if you're working on the Linux kernel, you're pretty much just using C (I think they were considering adopting Rust, but idk if that's still going on). And, of course, the dominant programming language for anything on the internet is Javascript (although WebAssembly has made huge strides in roughly the past decade, so you can actually use other languages as long as they can compile to WebAssembly).

Finally, to wrap up this already way-too-long comment: a lot of these languages are very similar to one another. They're all procedural, heavily inspired by C, and for the most part they're either compiled and statically typed, or they're interpreted and dynamically typed. There are also a whole bunch of other languages, called functional languages, that are designed based on entirely different principles (the principles aren't harder to learn than what you're having to learn for Java, they're just different). But if you are looking for a universal programming language, I think the closest you're going to get is either C, C++, Python, or Javascript. In addition to Java, I would strongly recommend you learn C and Python (C has a bit more of a learning curve, but it teaches you a lot about memory management, which is a lesson you'll carry with you to any other language).