Hi Maryam,

Apologies for replying late to this.

When a software project is say 5 or more years old, it sometimes happens the technology that was used to build it is not popular anymore, or that technology is even deprecated.

For example, around 2007 we used to build websites using ASP but then Microsoft released ASP.NET as their new standard way of building web apps.

A more recent example would be a web app built using Coffescript and Handlebars templates. We used this in 2012 at another company.

These are outdated technologies very few people use. Almost no one would choose these technologies for a new project today. It’s difficult to hire people who are a willing to use them, it’s difficult to find answers to problems online.

If there’s an old project that requires some minor maintenance, maybe a few days work, it’s OK to just go ahead an make those changes in the existing old codebase.

But if there’s a need for large changes, or large new features, it’s often easier and cheaper to rebuild the project using a new technology. You’ll be more productive and save money long-term because you’ll be able to make further changes and find people to work on it.

So this is why it’s common to throw away very old code (5, 7+ years) and rebuild.

Like with anything, there are exceptions. There are legacy systems for example at banks, military, that are decades old written in Cobol and they still have people maintaining those.