In this particular case it looks like they're just being asked to testify about their product in an unrelated case. They aren't being sued.
Call your lawyer first and do what they say. Most likely you can arrange a deposition more convenient to your schedule and location.
https://en.wikipedia.org/wiki/Strategic_lawsuit_against_publ...
but you can be labeled a "vexatious litigant" which causes you to be radioactive for representation (nobody wants to disbarred):
https://en.wikipedia.org/wiki/Vexatious_litigation
(IANAL but I enjoy watching them on TV)
A subpoena is just a demand for testimony. The court wants to "know what you know" so it can make a better decision. Testimony before courts of law is part of your civic duty as an inhabitant of a nation under the rule of law. Yes, it has costs. You have to bear them for the same reason you need to pay your taxes, because a civilization without courts isn't one we want to live in.
The only way to misunderstand this is to not have read the linked page. HN is not immune from headline-only outrage. The first paragraph literally ends with:
> ... in relation to the government's recent injunction against their acquisition of a VR fitness company.
If the answer is not Meta pays, then why isn't it?
And the practical reason is that poor people have the right to petition courts for redress of grievances too. You're upset because Zuckerberg happens to be rich, so this seems unfair. But what if the startup had to sue someone and needed testimony from someone else to prove their case? You think they should have to pay just to get facts before the court?
There are cases of this already happening in the case of poor people, otherwise vexatious litigants wouldn't exist.
I wonder if the judge even knew that one of the list of companies was "small company mctinypants" or just assumed all were massive and huge.