So, they really aren't that easy to bolt on, if not considered from the beginning. Monoliths, for example, are a real PITA to make reliable and scalable.

Worse, once your company is successful, there will be an endless list of features to add to your product, meaning nobody has the time to "bolt those features on". How the product begins, is how the product often lives on well past it's expected lifespan.

My apologies that the sarcasm was a bit too subtle - no they are not.

How is scalability easy to bolt on? Most companies end up rewriting their entires stack, multiple times.

Those are absolutely not easy to bolt on.

And security, that one's trivial. Just get an audit and fix whatever they manage to find, done!