I wondered this before joining a large tech company. As it turns out, a lot of engineering is done on experimentation to optimize the product. Only a small portion of users might see the experiment, and many don't succeed.
An example might be complying with food and alcohol law in a single region, which you would never see unless you lived there. Another example might be a complete experimentally gated refactor that shaves 1 second off loading time. A lot of effort would go into simply making sure the change can be turned off, and verifying with unit tests, which takes time and effort.
These projects might be pointless on a small app, but in a large business might be worth millions to the company.
Another aspect is your changes often have to be approved by a lot of people, which is not the case on small projects. Your projects are also analyzed by data scientists, to make sure they're not harming the business - and if they are, your work might be thrown out, which contributes to even less visible change to outsiders.
All of these in concert slow things down, and necessitate staff.
An example might be complying with food and alcohol law in a single region, which you would never see unless you lived there. Another example might be a complete experimentally gated refactor that shaves 1 second off loading time. A lot of effort would go into simply making sure the change can be turned off, and verifying with unit tests, which takes time and effort.
These projects might be pointless on a small app, but in a large business might be worth millions to the company.
Another aspect is your changes often have to be approved by a lot of people, which is not the case on small projects. Your projects are also analyzed by data scientists, to make sure they're not harming the business - and if they are, your work might be thrown out, which contributes to even less visible change to outsiders.
All of these in concert slow things down, and necessitate staff.