We have over twenty years of experience!
The application that is used for your website is defined by the function you have for it.
A corporate site would require a different application than an ecommerce store.
And we prefer using existing open source applications which are then customised
to your requirements instead of writing everything from scratch for two reasons:
Price: A ready application has 1000s of developers that contribute code, this allows us to save costs for you while using best of breed software. For example if you were to try and replicate a CMS with the functionality of WordPress and all the code addons (plugins) available for it, the cost would be in millions of dollars.
Time: Assuming you had millions to spend on your website, to replicate a codebase of the size of WordPress including features and add-ons would take you a couple of years at the very least. Not something you want to hear when you need a website yesterday.