There are some men who think they speak for all men who have ever existed (looking at you Jordan Peterson) and I also think there's a lot of toxic masculinity style peer pressure on other men to outwardly express an idealised or stereotypical version of woman.
I think plenty of men are genuinely attracted to women of all shapes and sizes. And then many more men are attracted to women they fell in love with whose bodies have changed over time.
Yes, some men fetishize obese women purely for their obesity but some men fetishize petite and skinny bodies too, but we don't go around saying all men who like skinny women are fetishists, do we? So there is some systemic fatphobia at play there.
Another point is obviously historical and cultural differences in the perceived ideal of a woman's body. There's been a huge rise and acceptance of how attractive "thickness" is as trends have moved on from the 90's and early noughties. And again the operative word is trends.
Once thing I will say that flies in the face of that, as unfortunately I do believe there are diminishing returns on this. As you look at bigger and bigger women you will probably get a smaller proportion of men who find them their ideal body type, and a bigger proportion of fetishists, but that goes for literally every physical characteristic possible. It's probably more noticeable with weight though as it's probably one of the largest ranges a human can have physically - you can be very skinny or absolutely massive, and that's not limited by any other factor.
In my personal experience, and I believe this is backed up by some science, is that weight distribution comes into play for determining how attractive a figure is moreso than weight (again up to a point). I've always had an hourglass body with a stupid amount of weight carried on the thighs and hips. I've had much male attention in my life, even at higher weights, and plenty of conventionally very attractive men interested. If you have a straight/apple shape, the excess weight might not be doing anything positive at all.
However I am at my highest weight ever and I do feel I get less attention, but there are also other factors at play so it's not really a truly fair comparison. I'm not saying I expect to have the same amount of attention now at a size 20 as I did at a size 12, but I've gone from having a lot of other stereotypically attractive traits (long hair, styled hair, pretty make up, nice clothes) to sterotypically unattractive traits (short damaged hair from bleaching, no time for makeup or hair styling most days, throwing on leggings and a t shirt because I WFH and don't have to make an effort).
So basically I don't believe for a second men aren't attracted to curvier women, I actually have a bias toward being curvier and find curvier women prettier myself, and I'm obviously not the only person on the planet who would feel this way.