For a sitcom, HIMYM had a few great seasons. However, the poor/illogical storytelling eventually caught up to the show. A lot of filler episodes, and they kind of wrote themselves into a corner.
The first one or two seasons of BBT weren't awful, until the characters started making drastic changes for inexplicable reasons. And that laugh track was absolutely grating, with Two Broke Girls being the only worse offender I can think of, with the laugh track playing after nearly every single line, regardless of it being a joke or not.
The biggest problem with these two shows, in my completely unsubstantiated opinion, is network interference. The higher-ups stop caring about making a good show, and care more about making a show with good ratings, which results in a general blandness, which is less appealing but appeals to a wider audience.
As far as people liking these shows, I used to be annoyed by it, but I don't really care anymore. They're neither high-brow humor nor intellectually-stimulating, but then again, neither is a lot of the stuff that I tend to watch.