I think the biggest issue people have is that SM isn't a 'point A to point B' type of anime. While that's not necessarily a bad thing, it takes on more SoL components that sagas before it which may not be everyone's cup of tea, especially when lot's of SoL anime give the impression that nothing is happening. There's a lack of urgency and while some plot points have been set up, they've not really been explored thus far.
Perhaps it's because there is no league. Ash didn't come to compete, he came to relax and only enrolled because he thought it would be cool. Considering how there isn't a sense of urgency in getting the badges before the league starts, people are put off.