Barcelona might lost their match El Clasico because they are playing with their rivals who will not give them the chance of winning the match. Also I will say that Real Madrid is more lucky this season than last season, so they had been lucky in most of their matches by winning it even when we don't expect it.
Barcelona actually lost the El Clasico even their youth player Yamal had an excellent match and is Man of the Match. This direct defeat means Barcelona will not be able to beat Real Madrid in La Liga competition. Only very few remaining matches and difference between two competitors is simply big enough, safe enough for Real Madrid.
Barcelona actually grew up some good young players in this season but they must look at Ansu Fati, Pedri and use their young players more properly next seasons. Young players are not strong enough physically and they are vulnerable to injuries which can destroy their career. If Barcelona want to build up a strong squad from their home-grown players, they must proactively protect their young players. Don't over use young players is best preventive method and Barcelona must do it.