Because when things go to court you need a meeting of the minds for a contract to be held up. It's accepted that people don't read contracts so the terms can't be far outside what people expect unless you've highlighted unexpected clauses, or shown that the person did actually consider the contract. It's one of the reasons, for example, you can't buy a house without having a lawyer representing you (in plenty of countries).
Equally, if the fine print the guest agrees to says the platform/hotel can cancel unilaterally, why should it be considered a problem?
> As it stands, only one of those two things was prominently mentioned on the website
Why does prominence matter?