this is the core of the problem between Devs and sysadmins. Sysadmins come from a mindset of a polished working system which never needs to change. They deliver stability and reliability to the business.
Devs come from a mindset to actively create change. This is to add new features and deliver new value and product to the business. As a Dev I do have to say that many Devs don't have enough experience in operations to understand properly how to help sysadmins, many don't understand the complexities of that job.
These two perspectives are at odds, and they should be. The new tools, like docker, start giving everyone what they want... Devs pick their dependencies, and in theory, can't stomp on the sysadmins pristine environment.
To respond directly to your question: because there are new things available in new libraries that allow us to develop new features!
The new things you need to develop new features are far and far between
99% of web software written these days could fulfil identical use cases on an IBM 3270 from 40 years ago. You enter something into a form and it gets stored in a database. You enter something into a field and it generates a report. That's all Amazon, Facebook, Google, any e-commerce site are.
Sure it might be nice to use a new version of that new JS framework that all the twitterati are going crazy about, but does it deliver value to the business that justifies the risk and investment?
And yet none of those things did arise 40 years ago. All of the nuances of all the code written since then make a difference, despite duplicating "identical use cases".
Devs come from a mindset to actively create change. This is to add new features and deliver new value and product to the business. As a Dev I do have to say that many Devs don't have enough experience in operations to understand properly how to help sysadmins, many don't understand the complexities of that job.
These two perspectives are at odds, and they should be. The new tools, like docker, start giving everyone what they want... Devs pick their dependencies, and in theory, can't stomp on the sysadmins pristine environment.
To respond directly to your question: because there are new things available in new libraries that allow us to develop new features!