He's only 22 years old. Next summer, he could potentially be a 23 year old coming off the back of a top season.
Baleba is young enough that his value is not going to be impacted too much by temporary bad form. One good season could easily make him a £100m asset in the current market.
From Brighton's point-of-view, there's no compelling reason to sell at a cut price at the moment. They're banking on him rediscovering his form and going for an extra £20-30m in 2027. It's what I'd be doing as well. Even if he only rediscovered a fraction of his form, it's still be worth it to keep him for another year.