I'm not sure I get this question. Which comedies are 'considered the best'. By whom? And who considers them boring? Because if it's just you, maybe a better question would be 'why am I unable to appreciate the so-called greatest comedies' or even 'why do people have different tastes'. Because while there are marks of objective quality when considering films, comedies are particularly subjective.
It depends to a great extent, as others have said, in what you are looking for from a comedy film. The laughter count does not necessarily correlate to the quality of the film, or even your enjoyment of a film. You can laugh a lot of times but still feel empty at the end of a film, or laugh only a couple of times but leave feeling warm inside with a smile on your face and want to watch it again.
But it's the two terms 'considered the greatest' and 'boring' that I wanted to pick up on. Because I just don't know who considers these so-called boring comedies the greatest (and you've only given two examples). Take a look at the
100 years 100 laughs list in the mofo lists section. Are these the films you're talking about. I've only seen 30% of these but a quick scan of those throws up some I found hilarious, and others I felt were dated, painfully unfunny or, yes, boring. And if I was thinking of films I preferred to those I would mainly be coming up with British films. Not because I think British films are necessarily better, but because as well as being subjective, humour can be quite culturally specific. Which is not to say you can't enjoy films from other cultures, but it ties in to the question of taste.
Age is a factor - things that were funny thirty, fifty, seventy years ago might not be considered funny now by modern audiences, although does this necessarily mean they don't deserve their spot in the cinematic canon? Topical satire can lose its bite. Racist, sexist or homphobic jokes could be seen as unacceptable (although considering some modern films, I'm not sure about this). Equally, some films retain their charm and feel as fresh today as they did when they were released (I'm guessing a bit here when talking about films released before I was born, obviously...).
So what are the better comedies that City Lights and Modern Times are considered better than? You really need to come up with some examples if your complaint is going to make any sense.
The most boring comedy film I've ever seen, by the way, is 'The Break Up'. I don't think this is critically acclaimed anywhere.