I don't think you have a solid grasp on the problem. To start off, Twitter did experienced major outages that it never experienced before. Also, you hire and retain people when you need to implement changes. If your goal is to cease any form of investment in your platform, like rolling out a new product or providing a new service, then your responsibilities are limited to keep the business barely aflost while coasting.
See it as a navy ship. You need full crew to perform all your missions, but mothballing the ship requires a skeleton crew.
Here you are, boasting that a ship doesn't require more than a skeleton crew to be kept afloat. I mean, sure why not? But are you saying what you think you're saying?
if you thinking you need 500s employee or something well you are wrong since many company do this for a long time and still do well
Discord is renowned for it's small engineering team, but I'm afraid you somehow claimed it has half the staff it does. A few years ago Steam reportedly employed around 90 engineers. Is it less than 500? I guess. What does that comparison tells you? Well, nothing. You need staff to roll out new features on multiple projects. If you add no feature, have no projects to work on, or have nothing to do then you don't need engineers. If your business plan has ambitious goals then you need engineers to achieve them. If all you're doing is keeping the lights on then you barely need anyone. Does this sound obvious?
I've been at companies that doubled their engineering staff overnight because they made a call to invest in a feature. I worked at companies that fired an entire floor of engineers because management decided some projects could be put on cold storage to improve financials. Why do staffing agencies are so popular? Have you ever thought about it?
it literally oblivious from the start and someone REFUSE to see the truth