I think it's more about people who are faithful viewers towards the TV Anime rather than people who select and pick and watch selective episodes imo. Although to be fair, SM had better TV ratings in it's first 20 Episodes than PM. SM even did better than XY&Z (Last 47 Episodes of XY).
@JinksChow how did the episodes of Sun & Moon after the Timeslot Change perform? I wonder if the numbers are high compared to these low Early-SM Numbers because that would confirm the suspicion of people not being able to watch the Episodes on Sundays.