like everything in life (and especially in Sonic games), it's close to (if not) impossible to please everyone. Lets look at a few aspects:
1) the automation of the levels: i could go on and on and on about how games have (mostly) been directed at casual gamers as of late, with overal difficulty levels going down over the years (achievements earned for completing basic actions, tutorial levels, little hints and helps everywhere. I dont remember there being any pitfall warnings in old sonic games at least.....or HELLO! I AM OMOCHAAAAAOOOO! Of course as the game industry slowly changes to please less dedicated players, stuff is bound to get easier. This is ONE way to see it. a second one would be that Sega (as shown lately) is having monetary difficulties (money problems) and might not have the resources to spend on the making of a Sonic level composed only of grand levels, filled with puzzles, well elaborated and long (the standart for long being for example, carnival night zone from S3&K, Egg Rocket Zone act 1 from Sonic Advance 1 and maybe classic planet wisp from SG). The third possibility being simple lazyness. It could also of course be a simple marketing strategy to launch games more frequently to make more money faster.
2) Difficulty in sonic games has always been.....how would i put it.....dubious...
im not saying its a bad thing but at least for me i usually dont even notice there is a difficulty option in sonic games.. i mean sonic isnt the kind of game where you can easyli change the difficulty. Why? well...how would you do it? you can increase the number of enemies and spikes and traps and whatnot....but thats about it. you cant increase the damage output of the enemies since in sonic there is no health bar and reducing the amount of lives avakiliable would probably seem unfair to some people. For example back in sonic 2 or 3 i never played in other difficulty other than the default one.... tho i noticed after trying easy that there was some facilitism at least special-stage-wise.
I dunno, it feels to me like sonic shouldnt even have variable difficulty to begin with.... it feels like the kind of game that should have a moderate difficulty with some hard parts here and there...... that being how the old games were. But as i wrote in 1) the casualisation of the market makes it so that sonic games are easy with a moderate part here and there instead. Casual players probably wont complain, normal mid-tier players (such as myself) might not complain and harcore gamers might or might not complain, since for hardcore gamers sonic isnt even about the difficulty in the first place but (at least as of late) more about the nostalgia. the only thing i see hardcore players doing in sonic games are speedruns, and i dont see them complaining about the games difficulty on that point, since they simply adapt to it. This is their way of having a "serious\hardcore challenge" in a Sonic game.....making a better time that other people.
"Boohoo the game is soooo easy because I can finish a level without dying in 10 minutes"