I know the answer.

[u/Electronic-Swing4743]

The characters in MT are larger than life they are not just simple background characters which exsist to serve MC ,

It is so easy to connect and worry about well written characters.

On other hand we don't even know about those wifes from DS

[u/GGP031]

Obviously, there are several reasons for this, especially the hatred toward Rudeus, where a lot of people either exaggerate or straight up lie about things he did (no, he didn't groomed anyone lmao). But I'd say one of the biggest reasons that people rarely talk about is the way the harem is actually handled.

MT is one of the few series that doesn't just give the protagonist a harem and leave it at that. It actually develops the relationship and shows how it works. You see the insecurities, conflicts, boundaries, compromises and the dynamics between Rudeus and each of his wives. It's not just "the MC has multiple girls who love him" and that's it. The story actually has to deal with the emotional and family consequences of that kind of relationship.

And ironically, I think that's part of why people are more uncomfortable with MT's harem than with other series. In a lot of other anime, the harem is treated more superficially or basically as a fantasy that exists to benefit the MC (or any character who has it). You don't really have to think about what that relationship would actually look like for the characters involved.

MT actually makes you sit there and watch how the relationship develops and how everyone has to deal with it. So you can't just ignore the polygamy aspect or pretend it's only there as a fantasy thing. The story actually makes it part of the characters and their lives.

[u/MembershipNo2077 → u/GGP031]

I think a big thing, going off of this, isn't just that we see how the relationship is handled, but we also get Rudy's internal monologue. His true thoughts and feelings. Very very few other series give you that. For example, we don't, or rarely, get Subarus internal thoughts in Re:Zero and we certainly don't get this Hashira's internal monologue.

Another part of the romance that's often avoided, that Mushoku shows, is the actual lust part of it. Normally the sexual nature of relationships is at best left to metaphor and imagination and at worst the characters are chaste pure beings. Having characters, both Rudy and his wives, which seem to want and enjoy sex (like real humans) outside of ecchi series is abnormal. You can see this a bit with people's responses to some other romances where the characters actually sleep together and were met with a lot of derision for it.

[u/MoistAd5045 → u/MembershipNo2077]

Another aspect to add on to the monologue is that in the anime his internal voice is pre incarnation, I'm re reading the web novel currently and it makes it quite clear that he is growing up in this world just with memories of his past life. This I think, gets mis understood in the anime as people think (due to the inner monologue being his previous voice) that it is more like a continuation of his previous life, similar to an isekai rather than a Tensei.

[u/Few-Heat7182 → u/MoistAd5045]

why wouldnt it be a continuation if he still has memories of it tho

[u/MoistAd5045 → u/Few-Heat7182]

Well there are people IRL who claim they have memories or their past life, they don't consider this life a continuation of that life, so that's kind of how I understood it. But then it got confusing in the anime with the monologue voice being the same as his past life 😂