> GPL is a theoretical idea that doesn't work in the real world, because in the real world, not everyone wants to or even can share their work products with everyone

In practice, that is wrong. GPL software is useful even in a corporate environment because you are required to distribute your modifications only to the users who you distribute the software to. So if your modifications are meant for internal use only, then it's perfectly fine to keep the modifications confined to internal distribution.

On the other hand, if you're talking about publicly distributing modified software with undisclosed modifications, then you're financially exploiting the labor of the original contributors. They did most of the work from which you derive monetary profits. The fair thing to do in such a case is to negotiate an alternate arrangement with the original contributors. Or you could opt to distribute the changes according to the original license, if that's an acceptable option.

I have seen GPL software used in corporate environments in both the manners described above, without any sort of legal or ethical concerns. But the avenue of unpaid labor is so enticing for many large tech companies, that they fearmonger against copyleft licenses as if they're the worst crime committed against open source. Their argument is that copyleft licenses are too restrictive. Restrictive to their financial ambitions, perhaps? Because I don't see them restricting the developers or the normal users in any manner.

> A very common reason as to why they aren't more popular is because they are often licensed with GPL.

They're unpopular simply because of the vilification campaigns I mentioned above. It was very popular at one time to diss on copyleft licenses without a discernable reason. That was until many realized that the permissive licenses, combined with CLAs were an easy avenue for many of those companies to extract free labor from them.