>>31718979SM is a very different game than the ones that the gen 1-4 fans are used to, likely due to the different system and changing nature of games.
Most notably, plot wise.
SM has a very plot focused singleplayer, focusing on the development of the characters and story through events such as Po town, the cosmog and Aether lines, etc.
Older pokemon titles had what are commonly known as "excuse plots," which are not necessarily a bad thing, as the minimal, undeveloped nature of the plot allows players to interpret more and project their own personalities and character types onto the blank slate characters in the game, since the only form of existing characterization is usually a single quote and the way they look. Similar examples include the original 2 Etrian Odyssey titles.
SM's established characters and emphasized plot rubbed fans that enjoyed having excuse plots the wrong way, as there is very little that one can project or interpret onto characters that have existing, developed personalities and the straight line plot is extremely contrasting to the open ended plot of older titles.
They are two extremely different methods but neither make any of the Pokemon titles bad games, just appealing to different audiences.