It's increasingly difficult for an episode of television to stand out. It's such a crowded marketplace, and most storytelling now tends to be so heavily serialised, that there's not quite the same emphasis on a single instalment.
Few shows now qualify as watercooler TV, where we'll ALL be talking about that one episode each week (Game of Thrones now stands pretty much alone in that regard), and binge-watching can mean entire seasons become a whole where all the episodes have blended together before you can even click 'play next episode'.
It can mean that certain shows with a strong season-long arc don't necessarily have one standout hour (or half-hour), but also that shows that might not be as good can still produce one or two great episodes, such is the level TV is at.
The amount of TV, which is no longer Golden Age but instead just way too much, means it's impossible to watch everything (my own big gaps this year include The Americans, The Terror, and Killing Eve (the latter of which is impossible to find in the UK), but also means that when one episode is so brilliant and memorable to rise above the noise, then you know it's really great.