American humour is too simple to be funny. Slapstick and toilet jokes may be enterrtaining for the first two minutes, but half an hour's worth palls to excrutiating boredom.
If the shows weren't remade the US 'humour' palate wouldn't be able to understand them. Of all the countries' humour I've experienced, the US' is the only one I don't find even remotely funny; it's too brash, common and arrogant. The French are sarcastic, the English are drily witty, the Germans are slow to laugh but highly sophisticated when they do, and the Greeks just think everything joyfully funny.
The only decent US TV show to make it over here was House; and that's only because they used one of our best actors to play the lead!
But to leave the America-baiting aside for a brief moment; there are tv shows which wouldn't translate well between cultures unless remade with a local spin, like the Office for example - (okay, so the US version sucks) the US work ethic is different from that present in the UK.
And don't forget that the European Victorians bowdlerised everything, like ignoring the beautiful Song of Solomon from the Bible, cutting the 'naughty' bits (Like the 'beast with two backs' in Othello) out of Shakespeare, and turning the good old-fashioned lurid, gory fairy tales designed to be a horrible warning to children about the real world, into a set of twee cute fables which had no relation to the originals (Mother Goose). And I've heard dire things about the Bollywood remakes of some films... (Haven't seen any so not going to go there!)
So it's not just the Americans - every culture picks and chooses what suits, even if it is at the price of ruining the original.