Just read this interview:
http://www.siliconera.com/2010/09/13/the-methodical-destruction-of-pokemon-in-black-white/The designs in Black/White may not be everyone's, preference, but there was a lot put into it. Gen 4 was considered the "Best" at the time, Masuda was trying to 1-up it, and you know what he did?
He was trying to make Black/White something that is for everyone. He wanted to make it for older fans who have already grown up... And new fans as well, introducing 156 new Pokemon so that can be "their" generation, they don't need to be overwhelmed by the previous 400+ Pokemon. Thats also why Masuda made it more linear, so its easier to follow, however there are a lot of places in the game and post game as well...
But then "Where's my Charizard or the 400 other Pokemon I want?". People where unhappy, they couldn't wait until post game to catch their favorite older Pokemon, they had a lot of hate for the new Pokemon and didn't like the sequel since it wasn't on the 3ds...
Dont you see? They all drove Masuda insane, so he started Kanto pandering like crazy in X/Y, Sun/Moon, and finally LgP/E. And there are less Pokemon because he doesn't want to "upset" people, that's why they keep on recycling old Pokemon with Mega Evolutions and Alola forms, because people want the "old".
