I mean they can be bought, but like almost any other club I'm sure they're just not dead keen on selling their best player on deadline day with no time to replace him for anything less than "fuck you" money.
Eze and Guehi will likely get early moves this summer and they'll have a big rebuild job on their hands, they've been sensible not to dismantle their entire team without the chance to bed in replacements and plan for life without Olise, Eze and Guehi all at once.