The Owls, Fulham and Reading – who Wednesday visit tomorrow in the Championship – all missed out on promotion as Huddersfield Town grabbed a place in the Premier League.
History books show teams have difficulties reaching back-to-back Championship play-offs, something the Owls have achieved in the last two seasons.
They lost to Hull City at Wembley two years ago, then were edged out by the Terriers in the semi-finals back in May.
Reading were beaten by Huddersfield in the subsequent final, and have toiled this season.
They sit in 19th spot – Fulham are marginally better placed in 14th – and have won just five games out of 17.
“Reading achieved the play-offs and the final last season, but so far they have not been up to that same level,” said Carvalhal.
“This shows it is not easy in this competition to get into the top six two seasons in a row, as we did, and we are trying to do again this year.
“Both Reading and Fulham reached the play-offs, but they are not finding it so easy this time.
“This may be because the expectation level goes up after you get to the play-offs.”
Wednesday, on the back of a five-game unbeaten run, travel to Reading in 11th spot, four points off the play-off places.
They snatched a 2-2 draw at Ipswich Town on Wednesday evening thanks to a rare goal from Kosovo international Atdhe Nuhiu.
He came off the bench, making only his third league appearance of the season, to head in Adam Reach’s stoppage-time cross.
Nuhiu has fallen behind strikers Steven Fletcher, Gary Hooper, Jordan Rhodes, Sam Winnall and Lucas Joao at Hillsborough, and his previous Owls goal was in February 2016.
“I haven’t been playing, it was not easy times, but I am still here,” he said. “You have to work hard every day in training.
“I have always kept working hard, that is what you must do as a player. It was just a goal, not more, not less.
“It went for me, the assist was very good, I haven’t played much football in the last while. I hope that can change, but in the meantime, I will work as in the same way as hard as I can.”