There is a better offer in the new contract that Nico Williams has so that makes him stay at Bilbao especially this is also a situation that could have been better because by being at Bilbao at least he does not have to think about competition for the line-up because he certainly already has his own place in the squad.
It's not the real reason, why did Nico Williams stay in Bilbao? I think this is due to Barcelona's U-turn to buy Olmo instead of him. Remember that Barcelona is still struggling with their financial. And, they have not yet registered many of their players in La Liga due to the financial condition.
Barcelona grew impatient with Nico, which is taking to long just to say yay or nay. They decided to target Olmo instead. It's not due to the larger contract offered by Bilbao. Bilbao made him a bigger contract. But, as a football fan, I must admit, Barcelona's offer looked sexier. Yet, Nico has decided to stay.
Looking at some previous rumors I think we know that there are several other clubs who want Nico Williams and it's not just Barcelona but when looking at the determination given by Nico Williams at this time who really wants more quality improvement to be even better, it is a suitable reason apart from Bilbao's desire to continue to provide more opportunities for this player and keep him from being pursued by any club.
This is a situation that is actually very good for Bilbao especially by looking at what is happening now it looks like Nico has started training again at Bilbao some time ago.
He is still very young for now so there are still many opportunities to be at a big club later, even though in terms of statistics and strength Bilbao is still below some big clubs in La Liga but that should be an opportunity for Nico Williams to make him more interesting in the performance he does because if his consistency is maintained, sooner or later more big clubs will want his services.
As long as Nico can still consistently perform at this rate, he will always be targeted by the big clubs. Some big English clubs are linked to him, but there are no updates on the rumor.
It now depends on Nico himself whether he can still make a good contribution to Bilbao this season or not. Because after all, at this time his performance will be increasingly glimpsed by many parties so that this moment is indeed a fitting moment whether he will eventually be forgotten because he cannot contribute better than before or again make a surprise by successfully performing better.