I'd say the two biggest factors are: 1. Change of resources / hardware / performance 2. Change of business requirements The first one should be clear. E.g. why

I'd say the two biggest factors are: 1. Change of resources / hardware / performance 2. Change of business requirements The first one should be clear. E.g. why does Java has arrays and primitives? Because they were needed for better performance. As hardware gets better and better, we can use slower techniques that give us other benefits, for instance development speed. The second one is trickier. For example scalability. It just wasn't an issue for most people some time ago, but now it has reached many more businesses. This means new problems occur, such as concurrency issues or failures that where negligible before. These need to be considered now and many newer languages offer techniques that deal with these problems better than languages before.