How does your villain feel about the PCs? Do they even know they exist? Are they aware of who is thwarting their plans and killing their lieutenants? Are they trying to stop them? Adjust for them? Recruit them? Do they think of them at all?
If not, maybe they should.
I don't mean this just as a means of making your game harder, but rather as a way of making the world feel more alive while also making your PCs actions feel more meaningful and like they're actually making a difference. And if you can sell that your PCs actions have meaning, it is easier to pull your players into the game world. And that makes everything more fun.
Consider the following: We have an adventure that starts with an attack on Village A, a delve in Dungeon B, and a bit of social and intrigue at Palace C. This is the chain the adventure goes on, three points where the PCs and the villain - or agents of the villain - can be interacted with.
Now, the way this goes most times is the PCs fight in Village A which gives them a clue that leads to Dungeon B which gives them a clue that leads them to Palace C. They follow the chain, figure out the plan, do the thing, and eventually try to foil the villain at Climactic Event D. There is nothing wrong with this. It is a simple but effective adventure chain that works.
However, consider the following. When the PCs get to Dungeon B there are some people that recognize them from the village and those henchmen retreat or otherwise go to get more people because they've seen what these heroes can do. Not only does this let you use more advanced tactics to spice up the encounter, but it also shows the PCs that the henchmen now fear them for how they did in the village and their actions carry over.
Now we continue, and after delving the dungeon and stopping the village attack, the PCs don't just show up at the Palace. They are invited. They're invited because the nobles want to hear of the attack on the village and the dungeon. Or because the villain wants to meet these people - and maybe have a chance to thwart them some other way.
Perhaps the PCs find a letter for the villain naming or describing them with a brief rundown of their known abilities and things to watch out for. Perhaps they're listed as "a potential real problem that needs to be handled." It's minor, it's fluff, it costs nothing and ultimately can mean nothing for how the mechanics of the adventure play out. But as a player it feels good. It makes you feel special. It makes it feel like the world is noticing your actions.
Give it a try. See how people react. Maybe it is worth the effort for your table. Maybe it is not. In my experience, it definitely is.