I remark on it because from the beginning it doesn’t answer “why do people like this kind of MC”, and to that point you haven’t answered it either. The lack of change makes it even more frustrating after all of this time.
You didn't ask a question, so I didn't answer any. (And even if you had, I would have assumed it was rhetorical, because knowing why other people enjoy it isn't going to change how you feel about it.) I was just baffled that you had somehow gotten up to this point and not realised that this isn't the kind of story where the MC will ever change from being a wimp. What are you expecting - for the dude to start looking like a baki character, to seek out fights against monsters and then also build a harem?
And to answer your question, why would I dislike the MC? He's a regular guy who isn't in any particularly good physical shape who has been thrown in a world with dangerous monsters and who just wants to enjoy good food, make easy money, and visit various places while staying safe. He's a sensible dude who doesn't like danger. He also considers Sui to be a very young child and gets worried and overprotective like many parent would. He's also a nice dude who cares about others, is friendly and has never displayed any personality defect besides being a bit cowardly (as in, he's never been an asshole to anyone). If he wasn't a fictional character, why wouldn't I want this guy as a friend?
With that said we aren’t talking about just any slime: you are massively underselling just how strong Sui is, not to mention literally blessed by a god and in the presence of Dora. If Sui is dropped and reaches terminal velocity, it can hit the ground and bounce back just fine guaranteed. The only threat would be if Sui was being actively thrown by Dora at high speeds, but 1. That most likely is not going to be happening because Dora has no reason to and 2. learning by experience would lead me to believe that Sui would get better and better over time.
The way you phrased it was that just being a slime meant it won't take fall damage, which is what I responded to. I already noted that Sui was strong and unlikely to get hurt.