What we find attractive has formed through eons of evolution, and we retain the preferences of those who managed to leave more descendants.
That's not the same as being more intelligent etc, but it's not completely unrelated either.
"Do you think this just happens?"
It comes more easily to some than others, but an hour at the gym is an hour at the gym, whether you enjoy it or not.
I say this as someone who mostly doesn't do the work, but I have plenty of friends and colleagues (and a spouse) who mostly do. It's effort and money and time and stress for them.
The same is true for money. It's still work to turn a million dollars into two million, but it's not anywhere close to the work required to turn a dollar into a million dollars. But nobody wants to be successful because of a lottery, so they'll argue that their father gave them "a small loan of a million dollars" but they made it big themselves.
The luck part isn't primarily about genetics [1], it's about whether you enjoy (or at least don't hate) the routines necessary to be attractive.
For instance: my wife sticks to a strict diet because she doesn't like having to make decisions about food. If you're lucky enough to be wired like her (I'm writing this next to an empty pizza box...), you can hit any goal weight and stay there. Our bathroom is covered in lotions and creams that she spends an hour applying before bed every night. I could not tell you their names, to say nothing of their purposes. She goes to the gym every day except for planned rest days, and does a workout routine that was decided on weeks ahead of time. I maybe go for a jog, if I remember to and I'm feeling up to it.
I've tried copying what she does, and I can't even stick to it for a day. But most women I know do some version of this, and all of the really attractive men do, too.
[1] sure, it is possible to really lose the genetic lottery, but unless you would've been a 19th century circus freak, the bottleneck is probably how hard you're trying, not your genetics
I'd also argue that there is a feedback loop, i.e. attractive people are told they're attractive starting at a young age, and so a large part of their self-esteem comes from being attractive, so they feel more pressure to do the things you mention, i.e. skin care, working out.
One of the advantages of not starting out on the "is attractive -> gets self-esteem from attractiveness -> tries to be more attractive" cycle is that as you get older you don't feel like you're losing anything. It's no fun when you're young, but that's a small minority of most people's lives.
I always wonder to what extent that attribution to slow evolutionary processes is true. There were several selective bottlenecks in our ancestry, and during historic times (from which we descend) most marriages were arranged, with attractiveness playing only a very small factor. Even in modern times, only a small percentage of the population had the luxury of breeding with a partner that we consider nowadays highly attractive.
Then there's the fact that up to 80% of marriages have been between first cousins or closer, which would would actually cause unattractive features.
So how come we think that sexual attraction is an evolutionarily shaped mechanism
There is also the feedback loop of "grooming", where, just like bees select a random bee to be groomed as a queen, humans are positively reinforcing a specific set of humans for reasons that have more to do with mass psychology than actual attraction. E.g. kings and queens are groomed as leaders and rulers, eventhough they are probably the most inbred and flawed genetic stock
Either because of cheating, or of sexual rites, or because of rape...
The Greek mythology are full of heroes descended from gods yet are raised by human kings married to their mothers, after all.
Attractiveness is a trait that signals health, not intelligence/social skill/etc.
That's why we evolved to desire attractive people.
It has nothing to do with being a marker for intelligence.
Genetic fitness means anything that results in more grandchildren in the end. Physical health is a big factor, sure, but so is intelligence and social skills.
Maybe this is in part a linguistic disagreement. By "attractive" I don't just mean "looks good in a photo", but any factor that attracts a partner.