I don't like bass tone that sounds like a dull thud, but that's just me.
that happens when you prefer the guitar

just kidding!
It seems to me that a great majority of TB'ers love flatwound strings.
as mentioned by others, it's mostly because these days flats are not the "standard" (although they "came back" a few year ago and now every brand makes flats), and since the 80's the "bass sound" shifted from the thick woody sound of flats to the bright and metallic sound of rounds.
so it's a bit normal that those in love with flats tend not just to be enthusiastic, but to spread the love; thanks to this, now every brand makes flats, some even in different ways, and they are not back on the shelves with new models, new attitudes and research results, like the "low tension flats" based on the Thomastik design.
it all depends on what you want and need.
generally people tend to think that flats are just dull sounding strings, but probably they never used them in the band mix, to find out that they don't need the upper highs to "shine through", and that flats have the perfect frequencies to stay exactly where the bass is supposed to be in most music genres, between the drum and the guitars.
rounds have more highs and basses, and give a metallic sound which sometimes is hard to separate from the guitars, and with too much basses and few mids sometimes it's just a "wooof" in the background; if the band needs that, it's perfect.
in my experience is easier to play with flats in a band mix without the need of equalization and much work, they are more "plug & play" in most situations, until you really need the metallic highs or the scooped mids that flats can't give.
these days flats are coming back even because many bands are using them, researching a "vintage" sound, like for example Bruno Mars bassist, which also slaps on flats.
in many "indie" bands flats are now the standard, because they sound vintage and smooth.
IMHO one should just try and understand what it's better for the situation: right now I have a Jazz strung with Labella 52-110 flats, a Gibson SG reissue with D'Addario nickel rounds and another SG Reissue with D'Addario Chromes.
they give me different sounds for different situations.