Please edit snarky swipes like "Ahh yet another person who" out of your comments here. As the site guidelines say, a good critical comment teaches us something.
Which systems are the "hard" parts? Given zero functionality change, how much larger can and should Twitter grow? Is the complication a function of ad revenue, volume of content, user traffic?
Just because you don't see functionality changing doesn't mean it isn't. Lots of new features, just not for the normal users. Not to mention all the backend work to make all this data flow around, be accurate, and be reliable.
And also, there's not just engineering. HR, Accounting, Lawyers, Trust and Safety, it's all there
The question is valid though as to why they've kept growing if the user-facing product hasn't changed. There are some good reasons but lots of bad ones too.
The point I'm trying to make is assume that user-side functionality stays exactly the same - frozen - for say 10 years. Given what you say above, it would be reasonable to expect the company to continue to grow in any case on its current 10-20% compounded annual rate with no end in sight. Is that truly sustainable?
Which users? Internal users? External users? External developers (I know, I know) or academics consuming their APIs? Advertisers?
Starting from the position of what don't I know about this situation, and / or what systems could cause it to be in this seemingly intractable state leaves you open to all sorts of new learnings vs. assuming there aren't intelligent, capable people on the other side.
Twitter is a platform that offers a product. Your attention is the product.
The part of Twitter required to maintain a decent stock of product has not needed to change outwardly, because it hasn't had to. There hasn't been a new version of human in a very long time. But even then, anything that creates more product (drives more engagement) means more revenue opportunity for the 90% of the platform you will never touch.
The parts of the product that theoretically make revenue for Twitter have changed significantly over time. Analytics, ad intake/spend, promotion for influencers/brands/etc.
Twitter is an advertising platform and it's the ads, ad targeting, advertiser tools that change. Doing new things with a large volume of data requires a lot of engineering.
"If you're not paying for the product, you are the product" as they say
It’s usually about the systems that serve the clients(the people who pay money to Twitter) and other parts of the company. They probably have a lot of internal system and corporate facing that change and evolve as the business evolves. Think contents management, legal, payments, BI, abuse prevention, systems performance, testing, growth, compliance, ads management for the customers and management for the ads purchases and performance, custom access to select people or clients and god knows what.
