Pedri could be that player. He is only 18 and is starting for both Spain and Barca. It took Iniesta and Xavi a few years into their 20's to get established so Pedri could well follow that curve.
They also have Ansu Fati who would have been part of the squad and possibly starting if not for injury. He is 18 as well and looks a top talent. I think he would start for Spain ahead of F Torres and Olmo.
My sense of it is for whatever reason, Spain's 'next generation' that was meant to emerge post their golden generation has never quite made it. In 2014, after they got dumped out of the World Cup at the first stage, they tried to bring through a new generation and there was a massive amount of hype about a lot of them.
Koke, Isco, De Gea, Bellerin, Thiago and Morata were all in their Euro 2016 squad and there was a lot of hope that they'd all to varying degrees be superstars. Statsbomb had an article that identified Morata as showing all the right thing for being one of the best players in the world. Carvajal, Saul, Rodri and Asensio were all in the World Cup 2018 squad and again, the expectations were sky high.
But you look at the squad for this tournament, and actually half of the above players didn't even make the cut.
Isco is now 29 and I don't think ever really even became a first choice player for Madrid despite having all of the hype in the world about him. Similar Asensio. Rodri has flattered to deceive since arriving on the scene at City.
Of all of this generation and a half of players, probably Thiago is the only one that's really lived up fully to expectations.
So is the answer that these players aren't good enough? I don't think it's as simple as that. With a couple of exceptions, ost of these players have been really good at various points at club levels - genuinely really high level performers for big clubs. They're not as good as Xavi and Iniesta were, but they're more than good enough to be expected to make it deep into every tournament, which just hasn't happened so far.