A bit of that as well, but I guess the somewhat lighter tone wasn't that much of a repellent. I suspect that the lighter tone (not goofy, but lighter than PoE) was established because of feedback from PoE and because the D:OS games have it and they were/are a big success. Again, no quote on or proof for that.
Anyway - I presume what @kanisatha meant - and what I mean - is that many "hardcore" CRPG players prefer a "Lord of the Rings" setting over a "Pirates of the Carribean" setting. I use those books/movies because they show a much bigger picture than I could paint just with a few words.
In PoE we also had a post-medieval, renaissance-ish world in the background, but it wasn't very obvious because the game took place in the Dyrwood... which is, culturally speaking, very different and fairly "behind" compared to some of the more advanced nations (Old Vaillia, Rauatai and so on).
Basically in PoE it's just the guns that remind you of it. That and some rare Vaillian haute couture...
The rest is gritty, quite dark, kind of backwards and medieval: the architecture, the common people, the items - even the tone is dark like the dark times (besides Edér, Hiravias, Zahua and Aloth sometimes). I mean Durance alone puts the whole setting back for at least a hundred years for the player.
In Deadfire all that stuff (overall presentation, architecture, clothing, even the weather) is obviously fitting the more "modern" and light setting of Pirates! (Arrrr!). There are some cool things mixed in to loosen it up, but you can't know that by simply looking at screenies and stuff at the storefront.
So - if you are not into that then you might be put off even before purchasing it. You can immediately see from screenshots and videos about the game what the setting is. This may influence your decision to give it a try. Lots of gamers really have to think about on what they want to spend their money. Lots of them are young and don't earn their own money - and if they do then it's probably not enough that they just can spend 40-50 bucks just to see if the game is nice despite that non-preferred setting. I would argue that if there are second thougths about the overall setting then that's bad for such game (which is not cheap compared to many others you might want to try).
That's just my highly subjective and speculative theory though.