They may seem that way to some, but they still provide a surprisingly versatile and useful user interface. Terminal programs and scripts are easy and fast to write, easy to interact with, easy to change, and trivially portable across POSIX platforms; hence, when writing a tool for oneself or another developer, most developers will usually opt for a CLI-based UI. Terminal program UIs are also very stable (in addition to being text-based), making them arbitrarily composable into scripts and workflows without fear of them breaking in the future.
Modern graphical UIs are usually easy to use, but they are far-removed from the code and tools that are used to write them or interact with their APIs programmatically. Terminal program UIs, however, are very close to the environment they're built in -- so the line between using a terminal program and interacting with it programmatically is delightfully blurred.
I use a multi-paned iTerm2/zsh window every day as a front-end developer (I'm on a Mac running macOS Mojave). I can't imagine working without it. There are a lot of good reasons npm, git, and other popular mainstays in modern development workflows are terminal-based.
That's because they're from the 70s, when literal terminals with no real computing power were connected to a centralized system that did all the work. They're archaic and silly.