If you've never worked on software development you need to understand that coding is not just grabbing random code and copy/paste it inside your own app and everything will work. Different architectures, different code-bases, different libraries (or same ones but in different versions), all require different approaches to get the puzzle pieces to work. If it was that easy, TX would have burped out an update right after atmosphere published the 6.2 key calc changes but they need to get everything working and with backwards compatibility. On top of that, enough changes are already in place with everything from the latest betas + bug fixing and all. Integrating core sig patching with new key calculations for 6.2 while maintaining the old code like cheat engine, xci loading and emunand also working is far from trivial. People are only concerned about 6.2 but this needs to work on all past versions as well.
Bear in mind that this is not TX related: they're just the target of this example. This applies to the majority of software development. Don't think for a moment that a 2 week cycle for a production (consumer ready) build is a long cycle! It's a pretty damn fast one. Stuff needs to be architected, implemented, old code refactored during this process some of the times, tested, bug-fixed, tested again and only then released.