Or put differently, what does Paradox actually do?
Their involvement in each of the games they're publishing (leaving aside the ones they develop internally) is probably different, but a few things that the "publisher role" can include that a distributor would not:
1) Being involved in decision making about what the game should be, specifically pre-release (and possibly before work really even starts at all). This may or may not be a "publisher actually has the authority" situation, but it often is.
2) Provide upfront funding (this is generally very "expensive" money for the developer in terms of the publisher's corresponding cut of the actual revenue).
3) Do most/all of the actual advertising/promotion/etc.
4) Work out distributor agreements. This used to be one of the most important parts: sure, you could develop a game, but how could you distribute it? Walmart doesn't talk to indies, they talk to publishers. Shareware/etc worked for some people, but it was hard to make a living. This is less important now with digital distribution, but even there getting on steam is not
an easy thing for an indie. Having a publisher like Paradox behind you makes that a lot easier.
5) Own the intellectual property and/or rights to produce sequels/expansions/etc (which may or may not include rights to the "story" part of the IP, code technology, etc).
As you can imagine, having a publisher can be both a great enabler and an incredible frustration. In theory it could be a great relationship if you were working with people with absolute integrity and who had confidence in you, but in practice there's a lot of... well, problems. I don't want to turn this into a rant. Your imagination suffices, I'm sure
There's a lot of indies out there, even among people who could get a publisher if they wanted one, and there's a reason for that.