I suppose it depends on what you consider the 'problem'. The fact Portugal had one of the easiest routes into the final ever having played Iceland, Austria, Hungary, Croatia, Poland and Wales to get there while Spain, Italy, Germany and France were cannibalizing each other? I think it's obviously a bit unfortunate and the seeding and bracketing can to some extent be blamed for it. However, it's also not unprecedented and not the reason the tournament kinda sucked.
I think we're just seeing an overall shift toward a more defensive approach to the game at the moment. I think one consequence of the principles of possession football championed by Guardiola and others becoming more widely used by talented, skilled teams in recent years is that it forces the less skilled teams in matches into a much more defensive default position in matches.
You don't slug it out vs such teams because you will lose. Managers have realized this. You form a layered curtain of defense, you alternate between sitting back with 8-9 players in your own box and periods of more aggressive midfield pressure. I honestly think people haven't talked enough about the revolutionary impact of shot blocking in football. It's as big a deal as it is in hockey. When I started watching football 30 years ago and up to maybe 7-8 years ago, blocked shots were quite rare and often seemed more coincidental. The idea often being that a blocked shot could be deflecting into goal as well.
Nowadays it's the ideal weapon vs possession teams and it's obviously something defenders' training is increasingly taking it into account as such. Blocks today aren't desperate last ditch measures, they're calculated tactics and used throughout matches. Possession teams are often stuck passing around the box without much effect because the opening they're looking for in the box is simply blocked by bodies. Meanwhile, the workaround of long-distance shooting is typically frustrated by shot blocking.
People laugh when a shot goes 10 yards wide, but they often forget that this is because the shooter cannot take any of the obvious shots because those won't get through on goal, so they try something fancier or simply run out of steam and just shoot to avoid a turnover. You kept seeing this with Germany, where players like Kroos, Ozil, Kimmich and Mueller kept moving the ball, looking for a shooting angle and simply not finding it as the defense consciously and in coordinated fashion moved their bodies into those shooting lanes.
In a worst case scenario, those blocked shots can initiate devastating counter-attacks as well. There's definitely a lot more method to it than there used to be. One can't really fault managers for building these kind of defensive bulwarks when the relentless attack by possession teams puts their somewhat less skilled teams on their heels to begin with. What makes this bad news for entertaining football is that this is no longer just happening when a top side like Bayern meet a much worse team like say Ingolstadt, but when a Germany meet an only barely less skilled France team who still fancy their chances a lot more playing on the counter attack while putting up a concrete wall around their box.