> put text on screen

I get where you're coming from but that's actually quite a bit of an oversimplification even for many web apps outside of the 1% for which a lot of modern web development solutions and frameworks seem to have been created.

For one thing it doesn't take any account of input. When someone draws something with Figma or writes something in Google Docs or buys something from Amazon - or indeed any online shop at whatever scale - or gets a set of insurance quotes from a comparison site or amends something in an employee's HR record or whatever it may be the user's input is a crucial part of the system and its behaviour.

For another, we're not just putting text on the screen: we're putting data on the screen. And whilst data can always be rendered as text (even if not very readably or comprehensibly), depending on what it represents, it can often be more meaningfully rendered graphically.

And then there are integrations that trigger behaviour in other systems and services: GitHub, Slack, eBay, Teams, Flows, Workato, Salesforce, etc. Depending on what these integrations do, they can behave as inputs, outputs, or both.

And all of the above can result in real world activity: money is moved, orders are shipped from warehouses, flow rates are changed in pipelines, generators spool up or down, students are offered (or not offered) places at universities, etc.