I haven't designed levels, but playing maps across a few games, I'm constantly amazed at how well small details are thought out. A seemingly random crate actually blocks off a line of fire that would give one team a major positional advantage; a tree breaks up the line of sight between two objectives; a decorative fire provides visual cover in an otherwise overly open lane; a curved passage has exactly the right proportions to give cover on one side while being open on the other, letting players choose when to engage.
In a well-designed map, every part has to play well with everything else, at least within line of sight. Even small changes to the layout result in unbalanced maps that lead to frustrating play. Randomly generated maps might be fun out of novelty, but they won't play well in the long run, at least for games like Counterstrike.
Compared to Fortnite, where every match is a unique experience with the addition of player-crafted buildings, and the static game map is under constant transformation each season.
On big budget games like Call of Duty, some of the multiplayer maps would be very finely tuned over thousands of hours of testing. A friend and I play regularly (just us against bots) and not a session would go past without either of us remarking that they'd nailed the maps. There's nowhere you can truly dominate a map. Everything has been tweaked to balance it all.
In a well-designed map, every part has to play well with everything else, at least within line of sight. Even small changes to the layout result in unbalanced maps that lead to frustrating play. Randomly generated maps might be fun out of novelty, but they won't play well in the long run, at least for games like Counterstrike.